Written by Aimee Bradshaw Reviewed by James Macey Updated on 3 June 2026 On this page SIP trunk providers in the UK 8×8 Flowroute Net2Phone What Are the Best Free SIP Providers in the UK? What Is SIP Trunking and How Does It Work? How Did We Rank the Best SIP Providers? Verdict: Which SIP Provider Is Right for You? FAQs Expand We may receive a commission from our partners if you click on a link to review or purchase a product or service. Learn More. According to our research, the best SIP trunking provider is 8×8, combining SIP connectivity with a fully integrated UCaaS platform, and allowing companies to manage voice, video, messaging, contact centre tools and Microsoft Teams routing within a single ecosystem.Flowroute also performed particularly well in our research, with its self-service tools, rapid DID provisioning and programmable routing capabilities making it especially impressive for organisations building tailored communications systems, rather than relying on out-of-the-box UCaaS software.As more businesses move to cloud-based VoIP (Voice over Internet Protocol) phone systems following the UK’s PSTN switch-off, SIP trunking has become an increasingly important part of modern business communications. This guide breaks down the best SIP trunking providers to help businesses choose the right solution for their size, and communication needs. The Best SIP Providers: Key Takeaways 8×8 is the best SIP provider overall. Its combination of SIP trunking, UCaaS features, global coverage, and Microsoft Teams integration makes it ideal for enterprises and hybrid businesses.Flowroute is best for developers and custom setups. Its API-first infrastructure, programmable routing, and self-service tools suit MSPs and businesses running platforms like Asterisk or 3CX.net2phone is strongest for budget-conscious businesses. Simple pricing and bundled VoIP tools make it a straightforward option for smaller organisations moving away from traditional phone lines.SIP trunking replaces traditional ISDN and PSTN phone lines. Businesses can make and receive calls over the internet while keeping existing PBX hardware and phone numbers.SIP trunking and VoIP are not the same thing. VoIP is the business phone system itself, while SIP trunking is the connection that enables external calling. What Are the Best SIP Trunk Providers in the UK?The best SIP trunk providers in the UK are 8×8, Flowroute and net2phone. Read on to learn how the three solutions compare when it comes to factors like IP features, third-party integrations, and price. 1. 8×8: Best SIP provider overall8×8 is a leading SIP provider which combines enterprise-grade UCaaS capabilities with advanced SIP and telephony infrastructure. Rather than managing separate providers for voice, contact centre, video, messaging and SIP connectivity, businesses can consolidate communications into one globally managed environment.This makes 8×8 a particularly good fit for enterprises operating across multiple offices, countries or hybrid work environments. 8x8 Pricing Bespoke SIP/VoIP quotes 8x8 Review Strengths Features both Teams routes (OC + DR) Global number footprint Mature documentation and encryption by default Weaknesses SIP price lists are bespoke Emergency-calling comes with caveats typical of IP voice (educate users and work out process) 2. Flowroute: Best SIP trunking provider for developersFlowroute is a SIP trunking provider built with flexibility and control in mind, making it especially well-suited to developers, managed service providers (MSPs), and businesses running custom communications infrastructure.Unlike traditional enterprise UCaaS platforms, it focuses on providing a lightweight, API-driven SIP layer that can be easily integrated into systems like Asterisk, 3CX and other programmable voice environments. Flowroute Pricing DIDs from around £0.37/month (depending on conversion rates) Get free quotes Strengths Fast DID provisioning, and developer-friendly configuration Strong API and self-service capabilities for routing Useful fraud prevention controls such as spend limits and rate limiting Weaknesses More carrier-focused than full enterprise UCaaS Support experience can vary on deployment complexity Less suitable for organisations wanting a single-vendor unified communications stack 3. Net2Phone: Best for small and budget-conscious businessesNet2Phone combines SIP trunking with a cloud-based VoIP and UCaaS platform, making it easier for businesses to consolidate voice, messaging and basic collaboration tools in one system.Due to its simple pricing structure and all-in-one managed service approach, it’s well suited to small and mid-sized organisations that want a straightforward, cost-effective move away from traditional phone lines, without the complexity of managing multiple telecom vendors. Net2Phone Pricing Custom Get free quotes Strengths Strong enterprise UCaaS and SIP portfolio Broad international coverage with global DIDs Compatible with major enterprise PBX vendors, including Cisco and Mitel Weaknesses Better suited to managed enterprise deployments than highly self-service SIP environments Integration depth may vary depending on CRM and UC stack requirements Pricing is generally bespoke and less transparent for enterprise SIP deployments What Are the Best Free SIP Providers in the UK?There are several providers that offer free SIP trunking, but these services can be of poorer quality than paid services. However, if your budget is very tight you could consider one of the following options:OnSIP provides mobile and desktop voice and videoconferencing.SIP2SIP offers audio, video, presence, chat, file transfer and conferencing.Antisip offers toolkits for mobile and desktop platforms.However, with so many excellent providers, businesses can shop around to find the best pricing and features to meet their needs.For organisations with existing PBX equipment, an option that works with the hardware already in place can save a great deal on initial set-up costs. What Is SIP Trunking and How Does It Work?SIP trunking is a digital technology that replaces traditional phone lines by using an internet connection to connect a business’ private branch exchange (PBX) phone system to the public network. To communicate with the outside world, businesses use trunking, which is in essence a pipe leading calls from the office to the public switched telephone network (PSTN).SIP trunking and VoIP phone systems are related, but they are not the same thing. A VoIP system is the business phone platform that people use day to day — handsets, apps, voicemail, call routing and integrations. SIP trunking is the connection that links that phone system to the public telephone network for external calls.In simple terms:VoIP = the phone systemSIP trunking = the calling connection behind itLearn more about the differences between SIP and VoIP.How has SIP trunking been affected by the Great Switch Off?The UK’s PSTN and ISDN networks will be switched off by January 2027 as businesses move to digital, IP-based communications. This means traditional phone lines are no longer suitable for modern business telephony.For businesses, SIP trunking has become a key replacement for older ISDN connections. It allows companies to make and receive calls over an internet connection while keeping existing PBX systems, phone numbers and call functionality in place.As a result, businesses should review their current phone setup and plan a move to IP-based telephony, if they have not already done so.What internet speed do I need for SIP trunking?The internet speed needed for SIP trunking depends on how many simultaneous calls your business expects to handle. However, as a general guide, each high-quality voice call typically requires around 100kbps of upload and download bandwidth.Speed is only part of the picture, though. A stable connection with low latency and proper network configuration is just as important for maintaining clear, reliable call quality. How Did We Rank the Best SIP Providers?At Expert Market, we spend time researching, testing and evaluating providers we write reviews about. This typically consists of conducting market research to narrow down the software that's really worth digging into a little more and then assessing it against a range of research criteria.Our decision-making criteria with assessment weightingInformed by readers and businesses we speak to regularly, as well as our own experiences using major VoIP platforms, we designed a research framework to assess each VoIP provider plan. It consists of eight overarching assessment categories, each designed to answer a specific question a buyer might have.Which VoIP service offers the best call handling features for UK businesses?Call management (25%): We assessed features like call routing, queues, custom greetings, voicemail screening and spam call blocking, to see how well each provider handles inbound traffic.Can this platform support internal communication across remote or hybrid teams?Communication channels (20%): We looked at the availability of tools like video conferencing, team messaging, SMS and mobile app functionality.Will this system help me onboard and train staff effectively?Training features (20%): We tested tools for live coaching (e.g. call whisper/barge), call recording and performance dashboards — crucial for service and sales teams.Is the pricing clear and competitive for small and medium businesses?Pricing (10%): We reviewed subscription tiers, user discounts, setup fees and whether unlimited minutes are included or capped.Will this VoIP system work with the software we already use?Software integrations (10%): We checked how well each provider integrates with platforms like Salesforce, HubSpot, Zendesk, Google Workspace and Microsoft Teams.Can we keep using our existing phones and hardware?Hardware integrations (5%): We reviewed compatibility with desk phones, speaker systems and headsets from major brands.What level of customer support is available if we run into issues?Customer support (5%): We tested the availability of live chat, phone and email support, as well as help centres and user communities.How secure is this system for business use?Security options (5%): We assessed features like multi-factor authentication (MFA), encryption and compliance with UK data protection laws (e.g. GDPR). Verdict: Which SIP Provider Is Right for You? Our in-depth research found that 8×8 is the strongest SIP trunking provider overall. It delivers the best balance of enterprise-grade reliability, global coverage, UCaaS functionality, and SIP infrastructure, making it particularly well suited to larger organisations managing hybrid teams, multiple offices or international operations.That said, the “best” provider ultimately depends on how your business operates and what level of control you need.If your organisation relies heavily on custom telephony infrastructure or in-house development, Flowroute’s API-first approach makes it the best option for developers and technically advanced teams. Meanwhile, Net2Phone is likely to appeal most to smaller and budget-conscious businesses looking for simplicity over complexity. FAQs How do I switch to a SIP provider? To switch to a SIP provider, businesses first review their current phone system, internet connection, and call requirements. Most providers can work with existing PBX hardware, helping reduce setup costs. Once you choose a provider, they’ll configure the SIP trunk, transfer your existing phone numbers, and test the system before going live. A stable internet connection is essential to maintain good call quality during and after the transition. How much do SIP providers cost? In general, businesses can expect to pay anywhere from around £10 to £30 per channel, per month, for standard SIP trunking services, although enterprise providers often offer bespoke pricing based on call volume and infrastructure requirements.Some providers, such as developer-focused platforms, charge separately for phone numbers (DIDs), outbound minutes and usage, while others bundle SIP trunking into broader VoIP or UCaaS subscriptions. Additional costs may also apply for setup, number porting, emergency calling or advanced call management features. Which type of business benefits most from SIP trunking? SIP trunking works particularly well for businesses that handle high call volumes, operate across multiple locations and want to reduce telecom costs without replacing their entire phone system.Larger enterprises often benefit from SIP’s scalability and international routing options the most, while SMEs can use SIP trunking to modernise communications gradually without major upfront investment. Businesses with hybrid working setups may also benefit from SIP-enabled flexibility and easier disaster recovery. Written by: Aimee Bradshaw Writer and researcher Aimee is Expert Market’s resident telephone systems and point of sale go-to. If she’s not writing about business products, you’ll find her daydreaming about dog walking on Dorset beaches. Reviewed by: James Macey Senior Business Software Researcher James has four years' experience as a researcher at Expert Market, covering categories from CRM to fleet management. He holds a Postgraduate Certificate in Social Research and spends hundreds of hours each month speaking to business owners and managers, as well as running product testing with the Expert Market team. Prior to Expert Market, he worked as a researcher in the construction industry