Compare SIP trunk providers by the calls your PBX needs to handle, the numbers you want to keep and the total bill. A monthly package, a simultaneous-call channel and a phone number are different things. The lowest advertised price does not tell you which service will cost least for your business.
This guide compares six UK SIP options: sipgate, Gradwell, Gamma, BT Business, Spitfire and Andrews & Arnold. We checked their published product information on 15 September 2026. Prices below retain the supplier’s advertised billing unit. Where a complete tariff or contract term could not be verified, we say what to request in a quote. Our recommendations reflect the documented service and buying requirements; we have not run comparative call-quality or uptime tests.
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- £4.95 is a package price - sipgate lists Starter by month; confirm incoming capacity, outgoing capacity, number charges and VAT separately
- Compare all 6 cost areas - include rental, calls, setup, number porting, PBX support and connectivity before deciding which offer is cheaper
- Check your exact PBX - get written confirmation for its model, software version and configuration before committing to a trunk contract
- Test before porting numbers - prove incoming calls, outgoing calls and the agreed failure route on a temporary number before migration
UK SIP Trunk Providers Compared
Use this table to identify a suitable product, then obtain matching quotes. Advertised starting prices are not complete monthly bills. We have not normalised prices with an unconfirmed VAT basis: ask each supplier to show both the net price and VAT on the written quote. Call charges and optional services can change the order of the shortlist.
| Provider | Published starting point | What the price or product means | Confirm before ordering |
|---|---|---|---|
| sipgate | Starter £4.95/month | A SIP-Trunk package, not a per-user subscription or a verified price for each channel | Incoming and outgoing capacity, number charges, calls and VAT |
| Gradwell | Advertises from £4/month | Headline starting price; request the channel and call-bundle breakdown | PBX version, channel quantity, setup, contract and VAT |
| Gamma | Quote required | SIP trunks with an optional call-management service to specify | Which features, bundles and support are included in your offer |
| BT Business | Quote required | Cloud Voice SIP connectivity for a compatible PBX | Current availability, PBX compatibility and the exact SIP product |
| Spitfire | Advertises from £4/month | Starting price on its SIP product page; obtain a current itemised tariff | Connectivity requirements, channel rental, setup and call charges |
| Andrews & Arnold | Bronze number: £1.50 + VAT/month in its effective January 2026 notice | Rental for a number; this is not a channel rental or a call bundle | Number class and current order price because public pages conflict |
Sources: sipgate prices, Gradwell SIP trunks, Gamma SIP products, BT Cloud Voice SIP documentation, Spitfire SIP trunks and A&A’s price-change notice.
Which SIP Provider Fits Your Business?
The right shortlist starts with what you already own and who will maintain it. If your business has a supported PBX and someone who can configure it, a trunk service can preserve that investment. If you need a complete phone system with apps and user administration, compare a hosted service as well. A cheap trunk does not replace all of those functions.
sipgate Trunking
Start here if you want a monthly SIP package and can manage the PBX connection. The published SIP-Trunk tariff lists Starter at £4.95/month and Regular at £8.95/month. The separate trunking product page describes monthly contracts, no setup fees and different incoming and outgoing call capacities. Those distinctions matter more than treating the package price as a universal per-channel rate.
The provider also describes using trunks across multiple locations, so a multi-site business should check the relevant configuration rather than assume it needs a different supplier. Its public pages distinguish trunking from its hosted PBX service. Check that the quote and order confirmation name the product you intended to buy.
What to ask: how many calls can arrive at once, how many can leave at once, and do those allowances share a limit? Get the charges for your existing numbers, the destinations you call and any services you need beyond the trunk. Ask whether changes in capacity take effect immediately and how a downgrade affects billing.
Our assessment: the published package structure makes sipgate worth comparing for a small PBX installation. It does not establish the cheapest total bill for a call-heavy team. Use a month’s real call records to cost the appropriate package, and test it with the actual PBX before porting a customer-facing number.
Primary sources: sipgate tariff and sipgate trunking product details.
Gradwell
Include Gradwell when you need a SIP option for a 3CX installation. Gradwell describes its trunks as 3CX-certified, with pay-as-you-go and bundled call options and a self-service portal. Its page advertises a starting price from £4/month. That headline does not provide enough detail to calculate a complete bill or assume every channel costs that amount.
Compatibility is a question about a specific system. Send Gradwell the PBX version, hosting arrangement and any session border controller configuration you intend to use. Ask which settings and features are supported, who will configure them and what happens when the PBX software is upgraded. A supplier’s compatibility statement is useful evidence, but it is not our own interoperability test.
What to ask: obtain the price for your required simultaneous calls under both pay-as-you-go and bundled tariffs. Specify landline, mobile and international traffic separately. Include number rental, porting, setup, the minimum commitment and support outside normal office hours in the comparison.
Our assessment: Gradwell belongs on a 3CX shortlist because it explicitly addresses that use case. Choose it only after checking the current support arrangement and the actual bill against another compatible trunk. Do not buy spare call capacity simply because your organisation has more extensions than concurrent callers.
Primary source: Gradwell SIP trunks.
Gamma
Consider Gamma when control of incoming calls is part of the requirement. Gamma describes SIP Trunk Call Manager as a service for managing inbound calls across numbers, including routing to alternative destinations. Its product information also mentions call bundles and fraud-management spending limits. The commercial offer needs to specify which of these services is included.
We have not verified a public standard price that can be applied to every Gamma proposal. Compare the quote for your business instead of relying on a generic price range. Where an offer comes through a partner, identify the company that bills you, the organisation that handles faults and the point at which an issue is escalated to the network.
What to ask: can your team change emergency call routing themselves, which destinations can be used and what are the diversion charges? Ask how spending limits operate and who can change them. Get the price of Call Manager, recording or other requested services separately from the base trunk.
Our assessment: Gamma is a relevant option for a business whose incoming numbers and continuity arrangements need active management. The value depends on the configured service and support contract. Before paying for advanced controls, define a failure scenario and have the supplier demonstrate the route you will actually use.
Primary source: Gamma SIP Trunking and Call Manager.
BT Business
Ask BT for a SIP-specific proposal if you want to connect an existing compatible PBX. BT’s Cloud Voice SIP documentation describes direct connection to a compatible phone system. This is a different buying requirement from a hosted phone-system subscription priced per user. A price for a BT hosted product should not be presented as the cost of a SIP trunk.
The documentation establishes the product and connection method, not a current universal tariff or an assurance that every new installation is eligible. Ask BT to confirm the currently orderable product for your site. Give it the exact PBX model and software version, the numbers to port and the concurrent capacity needed.
What to ask: request a line-by-line price for the SIP service, connectivity, installation, number migration, calls and support. Check the contract length and the cost of any required gateway or session border controller. Get written responsibility for diagnosing a fault that crosses the connection between BT and your PBX maintainer.
Our assessment: a BT proposal is useful where keeping the supplier relationship or coordinating an existing service migration matters. The comparison should be based on the specific offer. An existing supplier relationship can make coordination easier, but it should not substitute for a clear price and support agreement.
Primary source: BT’s Cloud Voice SIP connection guide.
Spitfire
Include Spitfire when you want to compare voice service and connectivity together. Its SIP page advertises service from £4/month and describes number porting, its own voice network and a Microsoft Teams Direct Routing option. These are product descriptions, not evidence that every installation includes the same connectivity or features at the advertised starting price.
Obtain a current written tariff. An older master price-list link was unavailable during our check, so we have not carried forward setup charges or contract discounts from that document. In particular, ask how the price changes when the service uses a connection supplied by Spitfire compared with an existing connection from another provider.
What to ask: confirm the unit behind the advertised price, how many simultaneous calls it buys, and the costs of number rental, connection, porting and calls. If resilience is required, have the supplier identify the alternate route and the circumstances in which it works. A second service that depends on the same failed equipment may not solve the problem you are buying it for.
Our assessment: Spitfire is worth quoting when the boundary between broadband and voice support is important to you. Compare the whole connectivity and telephony proposal, including any minimum term. A lower headline trunk price does not settle the value of a combined service.
Primary source: Spitfire business SIP trunking.
Andrews & Arnold (AAISP)
Consider A&A when you want direct control of a technically configured SIP service. Its SIP-trunk guidance describes pointing numbers at a PBX using SIP registration or a configured hostname. The service documentation says it does not impose a channel-count limit. That does not mean calls, numbers or the network capacity used to carry them are free.
There is a public pricing conflict to resolve before ordering. A&A’s dated notice sets Bronze number rental at £1.50 plus VAT per month from 1 January 2026. Some product pages still display £1.56 including VAT. Those figures are inconsistent. We use the effective-dated notice as the stronger pricing reference and recommend confirming the current order price and number class.
What to ask: check the rental and setup cost of each number, the outbound tariff, call limits or fraud controls and your expected peak traffic. Ask how incoming calls should route if the PBX cannot be reached. You also need an administrator or maintainer who can own the configuration and test it.
Our assessment: A&A deserves a look for a business with technical support that wants this style of service. Per-number rental can be attractive, but it cannot be ranked directly against a channel package without including traffic and the required support. Confirm the documented price discrepancy in writing before making a cost decision.
Primary sources: A&A SIP trunk guidance, VoIP product information and effective January 2026 price notice.
How Much Does a SIP Trunk Cost in the UK?
The cheapest advertised UK SIP trunks start at about £4 a month, but that is a package price, not a full bill. Gradwell and Spitfire both advertise from £4/month, and sipgate lists its SIP-Trunk package at £4.95/month for Starter and £8.95/month for Regular, on monthly contracts with no setup fees. Gamma and BT Business supply quotes only, so their prices cannot be compared from public pages. Andrews & Arnold lists a Bronze number at £1.50 plus VAT per month, which is a number rental rather than a channel or call bundle.
These headline figures are not like-for-like. A package may cover a set number of simultaneous calls, while number rental, call charges, setup, number porting and PBX support are billed separately, and VAT is not always confirmed. Our worked example below shows a quote with the higher monthly price can still have the lower first-year cost. The cheapest trunk is the one with the lowest total for your own call volume, numbers and contract length.
Build a total monthly figure from the same requirements for every supplier. Separate the recurring bill from the one-off migration bill. Include charges already paid to a PBX maintainer or connectivity supplier as well as the new trunk quote. Otherwise, a service that leaves more work and cost with your business can appear cheaper simply because those items are missing.
| Cost item | What to request | Why it changes the comparison |
|---|---|---|
| Trunk or channel rental | Capacity, direction of calls and billing unit | A package may distinguish incoming and outgoing calls; user count is not channel count |
| Number rental | Each number or number block, including any special number class | A low trunk price may exclude the numbers customers actually dial |
| Calls and bundles | Included destinations, pooled minutes, out-of-bundle rates and minimum charges | The same rental can produce a different bill for a busy sales team |
| Setup and porting | Installation, transfer fees, rejected-order charges and test arrangements | One-off costs affect the first year even when monthly rental is low |
| PBX and equipment | Licences, maintenance, gateways and session border controllers | A trunk does not provide every phone-system function or remove maintenance work |
| Continuity and support | Backup route, diversion charges, support hours and fault ownership | The service needed during an outage may be an additional charge |
| Connectivity and contract | Required broadband, commitment, annual changes, exit charges and VAT | A discount can depend on buying another service or staying longer |
A worked example of the comparison method
This is an illustrative budgeting example, not a supplier tariff. Suppose a business needs five concurrent-call channels, ten numbers and a known monthly call allowance. Quote A charges £5 per channel, £1 per number and £20 for the required calls. Its recurring subtotal is (5 × £5) + (10 × £1) + £20 = £55/month. If setup is £100, its first-year subtotal is (12 × £55) + £100 = £760, before any other required services and VAT.
Suppose Quote B offers the same documented capacity, numbers and calling requirement for £60/month with no setup charge. Its first-year subtotal is £720. In that example, the higher monthly price has a lower first-year subtotal. In a later year without setup, Quote A would have the lower subtotal if all other terms stayed the same. This is why the contract period and included services must accompany the headline price.
Replace every assumption with written figures from the suppliers you are considering. Do not use the example as a market estimate. If one proposal includes a PBX licence or an internet connection and the other does not, add the missing service before comparing them. Keep an explicit column for charges that remain unconfirmed rather than silently treating them as zero.
Our business phone system cost calculator can help organise a broader system budget. Use current supplier quotes for the trunk-specific inputs. For a wider comparison of phone-system types, see our business telephone systems guides.
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SIP Trunking or Hosted VoIP?
Choose the architecture before comparing the monthly prices. A SIP trunk connects a phone system to the telephone network. Hosted VoIP normally supplies phone-system functionality as a managed service. The choice is therefore about which equipment, software and administration your business wants to keep, rather than whether one headline price is lower.
| Your situation | Start by comparing | Decision to resolve |
|---|---|---|
| A supported PBX already meets your needs | Compatible SIP trunks | Can the existing system be maintained through the proposed contract? |
| The PBX needs replacement and staff need calling apps | Hosted business phone systems | Does the subscription include the functions and support you need? |
| Your IT team runs a software PBX | Supported trunks plus hosting and maintenance | Who owns upgrades, security, backups and fault diagnosis? |
| Staff want calls inside Microsoft Teams | A documented Teams calling design | Which licences, connection service and administration are required? |
| You have several sites or customer-facing numbers | A design for routing and continuity | What happens to incoming calls when one site or system fails? |
For a fair financial comparison, include the life of the existing PBX and the work needed to keep it supported. A business that already pays for capable IT support may make a different choice from one relying on a non-technical office manager. Both need a clear support route, but they may buy it in different ways.
Do not assume a standard SIP trunk automatically delivers Microsoft Teams calling. Ask for the exact proposed architecture, licensing and support responsibility. Likewise, a hosted phone subscription should not be substituted into a SIP price table as though its per-user charge bought the same service. Compare complete designs that meet the same requirement.
If you are replacing the phone system as well as its connection, use our UK VoIP provider comparison alongside this guide. Keep the decision about retaining the PBX separate from the supplier’s discount for signing a longer contract.
What Should You Check Before Choosing a SIP Trunk?
Specify peak simultaneous calls, then test the proposed service on your network. Do not allocate one trunk channel to every employee by default. Ask your current system administrator for call records showing the busiest periods and any blocked or queued calls. Allow for the way transfers, conferences, diversions and outbound campaigns use capacity in the proposed design.
Confirm the PBX connection
Give each supplier the PBX manufacturer, model, software version and hosting location. Ask whether support uses SIP registration, IP authentication or another documented arrangement. Confirm any gateway or session border controller requirement and which party configures it. Keep a copy of the supported settings and a named contact for changes.
Compatibility should cover the features you use, not merely a completed test call. Check caller ID presentation, incoming number routing, voicemail, hold, transfers, conference calls and any contact-centre functions. Where your business depends on a fax device or another specialist system, ask its maintainer for an appropriate supported replacement or connection method.
Test the network during a busy period
Ask the supplier to size bandwidth for its supported codecs and configuration, including protocol overhead and simultaneous traffic. An advertised broadband download speed alone does not establish whether voice will work well. Upload capacity, delay, variation in delay and packet loss can all affect calls. A test when the office is empty may miss problems that appear during normal work.
Run the test while other business applications are active. Confirm firewall settings, any address requirements and whether traffic management is needed. Record which party owns changes to the router and who can diagnose a problem that affects only some calls. This evidence is more useful than an unsupported claim that one brand always has better call quality.
Define the failure route
Write down what must happen if the office loses power, the internet connection fails or the PBX stops responding. Ask whether incoming calls can be redirected at the provider level and whether your team can make that change without the failed PBX. Confirm which numbers and destinations are covered and what diverted calls cost.
A resilience proposal should explain its dependencies. If two connections share the same router, power source or underlying route, ask which failures the second connection actually protects against. Test the agreed scenario before relying on it. A service-level agreement can define remedies, but it does not make a business continuity plan unnecessary.
Agree security and administration
Ask for the supplier’s recommended authentication, permitted destinations, fraud controls and spending limits. Decide who can make changes and how access is removed when staff or maintainers leave. Keep the PBX supported and assign responsibility for updates and backups. Avoid publishing connection credentials in migration documents shared outside the people who need them.
Agree how emergency calling and the registered site address work for the proposed service, including for remote users. Follow the supplier’s prescribed validation process. These questions belong in the design and handover, alongside ordinary incoming and outgoing call tests, rather than being left until the previous service has been cancelled.
How Do You Move Existing Numbers to SIP?
Plan the migration around the numbers and services you rely on. Begin with an inventory of main numbers, direct-dial ranges, broadband and any devices attached to the old service. Ask the existing provider and each device maintainer what depends on that connection. For the wider migration context, see our PSTN switch-off guide.
- Confirm ownership and dependencies. Match the account details and numbers on the current bill with the port request. Identify any service that could be affected by moving or cancelling the line.
- Prove the new design. Use a temporary number to test the PBX, network, call routing and agreed failure route. Resolve problems before the main number is moved.
- Agree the port plan. Get a proposed date, escalation contact and procedure for delays or rejected requests. Do not assume a requested date is a confirmed appointment.
- Test the ported numbers. Check incoming calls from different networks, outgoing caller ID and the internal destinations. Include the important direct-dial numbers, not only the main switchboard.
- Close the old service carefully. Confirm that the port has completed and dependent services are safe before instructing cancellation. Retain bills and the completed handover record.
Set a business owner for the migration as well as a technical contact. Staff need to know what changes on the day, how to report a failed call and how to reach the support team. Put the temporary contact route somewhere accessible if the phone system itself is unavailable.
SIP Trunks for Home Use and “Free” Offers
A SIP trunk connects a phone system (a PBX such as 3CX, FreePBX or Asterisk) to the telephone network, so a home user without a PBX usually has nothing to attach one to. If you work from home and want a business number, a cloud phone app is normally the simpler route, and our VoIP providers comparison covers those. Every provider above publishes a paid package or quote, and we did not find a verified free tier among them. Treat any “free” SIP trunk as a trial or test service, and check the call capacity, number charges and what happens to a ported number before relying on it for business calls.
Our Recommendation
Request two or three comparable proposals for a written requirement. For a monthly package, start with sipgate. For a 3CX installation, include Gradwell. For inbound call-management needs, include Gamma. Compare BT and Spitfire where the wider connectivity or supplier arrangement matters. Consider A&A where you have technical support for its SIP configuration and can confirm the current number tariff.
These are shortlisting suggestions, not results from an independent performance benchmark. Ask the same questions of every supplier, test the chosen service and compare the contract-period total. The best option is the one that supports your actual phone system and calling pattern at a clear cost, with an accountable support arrangement.
Keep the supplier’s final quote with the capacity, number list, call assumptions, VAT treatment and support commitments attached. That gives you a useful reference when the first bill arrives and when the contract comes up for renewal.
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