SIP Trunking is the fastest-growing telephony service and Crystaline are the expert SIP Trunk providers of one of the UK’s leading solutions.

Crystaline’s Session Initiation Protocol (SIP) Trunks provide a highly-flexible alternative to traditional landlines and are compatible with all the leading IP Private Branch Exchange (PBX) brands in the UK market, giving you peace of mind.

Compared to traditional landlines, Crystaline SIP Trunks are cheaper on a per-channel basis and more flexible in terms of what telephone numbers you can have and the locations in which you can have them. In addition, they are quicker to install and offer a robust business continuity service that ensures your business never loses any calls.

Our service can support connections ranging from two channels for businesses, with no limit on the number of channels that can be supported for large enterprises and contact centres.

How does it work?

Crystaline SIP Trunks connect your PBX to Crystaline’s network, enabling full PSTN breakout on the public telephone network. Connection from your site (or sites) to our network is via an IP connection (for example broadband or Ethernet) and is delivered as an end-to-end service with an availability guarantee, voice channel guarantees and voice Quality of Service.


The Benefits of SIP Trunking


Flexibility with phone numbers. SIP trunking enables you to move office and keep the same geographic number without any ongoing call-forwarding costs or those associated with producing new company stationery.

Save Money

IP connectivity costs less than ISDN with lower call costs, free internal calls between extensions and offices and lower line rental costs for multi-sites. Also, no expensive call-forwarding costs are required should you relocate or need to divert calls in the event of a disaster.

Business Continuity

If your office has to be temporarily relocated in an emergency, this can be achieved quickly and cost-effectively with SIP trunking to keep your business working.


SIP trunking provides a phone service that will cope with any situation and give you business-grade resilience for your telephony. Whether you need to keep your business running in a disaster or emergency or you need to load balance your calls between sites during peak hours, SIP trunking delivers.

Line Rationalisation

For businesses with multiple sites, SIP trunking provides the opportunity for line rationalisation and reduces the number of PBXs you need to maintain – while retaining full control of the numbers associated with your business.


Compatible with Skype for Business and Microsoft Teams. Crystaline SIP Trunks are integration tested and approved to interoperate with Microsoft allowing you to directly connect to the MS platform to make external calls.