SIP trunking from Crystaline

SIP trunking

Office phone systems have traditionally used the Integrated Digital Service Network (ISDN) or the internet, through Session Initiation Protocol (SIP) trunking. SIP trunking is a service that allows businesses to access the benefits of modern telephony solutions, like hosted VoIP, using a traditional Private Branch Exchange (PBX) phone system. A PBX system is a private telephone network used within an organisation, like an office phone system. 

From 2027, ISDN lines will no longer work due to the switch off of the Public Switched Telephone Network (PSTN). Therefore, businesses are left with no choice but to switch to an internet-based phone system. It’s possible to upgrade your existing office phone system and hardware through SIP trunking.

How does SIP trunking work?

SIP trunking is a protocol that connects a traditional PBX phone system to your provider’s, such as Crystaline’s, network, enabling phone calls without relying on the PSTN. A SIP trunk acts as a virtual phone network that uses an internet connection — typically business broadband or Ethernet leased lines — to link your business to Crystaline’s network.


Once the SIP trunk is in place, traditional office phone systems can be used for end-to-end communication through voice, video and chat.

SIP trunking | Office phone systems | SIP trunk services

Why upgrade your legacy office phone system?

  • Flexibility

    SIP trunks are not bound to a single location, which enables you to move office and keep the same geographic number without any ongoing call forwarding costs or the need to purchase a new office phone system.

  • Cost efficiency

    SIP trunks cost less than an ISDN system. There are lower call costs, free internal calls between extensions and offices and lower line rental costs for multi-sites. There’s also no need for expensive call forwarding costs should you relocate, or any need to divert phone calls in the event of disruption.

  • Mobility

    Voice calls can be easily routed to a mobile device. Whether you’re working from home, the office or on the go, you’re contactable through the same phone number.

  • Business continuity

    If your office has to be temporarily relocated due to an emergency or disruption, SIP trunking keeps phone lines operational. If there’s a power outage or system failure, or you need to load balance your calls between sites during peak hours, it diverts voice calls to an appropriate, accessible number.

  • Streamlined system

    For businesses working across multiple locations, SIP trunking provides the opportunity for line rationalisation. It reduces the number of telephones that need to be maintained, while still giving you control over the telephone numbers that are associated with your business.     

  • Compatibility

    SIP trunking allows businesses to use the same internet network for various communication services, which supports the migration to a unified communications system. Crystaline’s SIP trunks are fully compatible with Skype for Business and Microsoft Teams, allowing you to directly connect to the Microsoft platform to make external calls.

Crystaline’s SIP trunk services

Crystaline SIP trunks are a cost-effective solution to modernising legacy office phone systems. Available on a per-channel basis, we offer businesses flexibility on telephone number and location. With quick installation, and an expert team on hand throughout the process, SIP trunking ensures your business never misses a call.

There’s no limit on the number of phones our SIP trunk service can support. Whether there’s two phone lines in one office or thousands of lines across a multi-site contact centre, SIP trunking can future-proof your phone system in preparation for the PSTN switch off and beyond.

If you’d like to discuss whether SIP trunking is the right solution for your business, get in touch with Crystaline here.