The clock is ticking. By January 2027, BT is switching off its Public Switched Telephone Network (PSTN), meaning every business still relying on traditional phone lines needs to make a move. This isn't just a minor upgrade; it's one of the most significant telecom decisions facing UK businesses this decade. The good news? SIP trunking offers a robust, internet-based alternative, replacing those costly ISDN lines and future-proofing your communications. But with so many options, how do you choose the right provider?
We've spent hours digging into the details, comparing ten of the top SIP trunk providers in the UK. Our focus? Transparency in pricing, the clarity of your calls, how well they handle outages, their compatibility with tools like Microsoft Teams, and crucially, how smoothly they can guide you through the PSTN migration. Whether you're running a sophisticated 3CX server, an Avaya IP Office, or a Cisco CUCM, the right SIP trunk provider can make all the difference.
The Standouts for 2026
When we looked at the landscape, a few names consistently rose to the top. For sheer clarity in pricing, sipgate is a breath of fresh air. They're one of the few major UK providers that actually publish their full pricing online, starting from a very accessible £4.95 per month. No hidden fees, no endless sales calls – you can sign up, set up your trunk, and be making calls. Their plans are straightforward, with free inbound calls on all tiers and monthly rolling contracts, offering fantastic flexibility. While their UK mobile rates are a tad higher than some, their transparency and ease of use are hard to beat. They also offer a free 30-day developer trial, which is a nice touch.
If you're a business heavily invested in 3CX, then Gradwell should be at the very top of your list. They're a 3CX Titanium Partner, which means they have certified compatibility and pre-built templates, making integration a breeze. Their pricing starts at a competitive £3.99 per channel, and they offer Microsoft Teams Direct Routing, ISO 27001 certification for security, and a solid Trustpilot rating. They've been around since 1998, so they bring a wealth of experience. Just be aware that the best rates often come with longer contracts, and their peak UK mobile rates can be on the higher side.
For larger, multi-site enterprises, Gamma stands out as the UK's largest independent telecoms provider. While they operate exclusively through resellers, their scale and reach make them a powerful option for businesses needing robust, enterprise-grade solutions. Their pricing is typically quoted per channel, falling in the £5–£10 range, and they cater to complex network needs.
Other Strong Contenders
BT Business, as the incumbent, offers a sense of familiarity and trust, though their pricing (£13/trunk) and contract lengths (12–36 months) are less flexible than some newer players. They offer both direct and channel options.
Spitfire focuses on an end-to-end network, providing a strong proposition for businesses that value a fully managed service, with pricing around £4/channel and contracts from 12–36 months.
For those with a more technical bent, AAISP offers incredibly competitive pricing at £1.56 per number on a monthly rolling basis, making them ideal for technical teams who want granular control.
8x8 offers a hybrid UCaaS (Unified Communications as a Service) and SIP solution, priced around £12 per user annually, appealing to businesses looking for integrated communication platforms.
Zen Internet bundles connectivity with their SIP offerings, providing a convenient all-in-one solution with quote-based pricing and 12–36 month contracts.
Finally, NFON is worth considering if you're migrating from a legacy PBX system, offering specialized solutions, though they primarily work through resellers.
Making the Right Choice
Choosing a SIP trunk provider is about more than just cost. It's about reliability, support, and ensuring your business communications can adapt and grow. With the PSTN switch-off looming, now is the time to explore your options. Consider what matters most to your business – transparent pricing, specific platform compatibility, or a comprehensive managed service – and use this guide to start your conversation.
