The Best SIP Providers in the UK

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According to our research, the best SIP trunking providers are 8×8, FlowRoute, and Net2Phone.

As VoIP (voice over internet protocol) phone systems become the norm, businesses have had to learn a new set of terminology. Session Initiation Protocol (SIP) is a standardised set of communication formats used in VoIP, instrumental in the sending of voice and video messages over a VoIP phone system. In recent years, SIP trunking has replaced standard phone system trunking, bringing a higher level of efficiency and quality to calls.

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What is SIP trunking?

Many business phone systems are hosted on a Private Branch Exchange (PBX), which eliminates the need for an individual line to be run to each desk in an office. 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).

The PSTN network will be switched off by December 2025, which means phone lines will need to be switched over to a digital network.

SIP trunking allows a business to make full use of an IP-based PBX, replacing traditional PSTNs with a PSTN from an internet-based SIP trunk provider. In the process, an SIP trunk can reduce a business’s overall costs and improve reliability for video conferences. For this reason, many businesses are making the switch.

Learn more about the differences between SIP and VoIP on our page.

SIP trunk providers in the UK

Businesses today can choose from a wide variety of SIP trunk providers, many of which offer affordable, high-quality services.


Quick overview

8×8 offers free point-to-point calling between a business and other 8×8-enabled sites, as well as unlimited concurrent calls. 8×8 also offers virtual numbers, which means local numbers can be set up in a variety of cities to make it easier for customers to call for assistance. The company’s SIP pricing is based on a business’s unique needs, with prices changing as a business grows and more numbers and features are added.


Quick overview

Developed by telecom-savvy developers, FlowRoute is designed to provide simplified, scalable, and direct access to a global network of VoIP users. FlowRoute offers phone numbers for £0.90 per month with outbound rates at £0.0070 per minute. The system uses detailed routing intelligence to manage calls for more advanced phone system functionality.


Quick overview

Net2Phone is an internet-based calling service that works with any PBX phone, making it ideal for businesses that already have PBX equipment in place. The service offers unlimited concurrent calls, no monthly contracts, and high-quality, low-cost calling. Customers pay as they use the service, with simplified, per-minute pricing that might be more suitable to businesses with low call volumes.


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.

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.

Written by:
Aimee profile image
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 thinks all businesses can improve if they use the right technology. At Expert Market, he utilises his 4+ years experience as a researcher to offer specialised advice on a wide range of categories from CRM to Fleet Management.