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SIP Trunks vs. ISDN

There are many reasons for businesses to choose to move from ISDN lines to SIP Trunks and cost is just one.

BT have publicly announced plans to turn off their ISDN network in 2025, which means that all existing ISDN connections will need to be replaced.


SIP offers the same voice quality enjoyed by ISDN services today, with advanced flexibility and Business Continuity Services.

Migrating to SIP doesn’t need to be expensive and can in many cases be delivered directly to your business, without making any changes to your existing telephone system, using our very own ISDN replacement service.


SIP trunks are cheaper than ISDN Channels and when you choose Southern Communications the rental costs include calls to UK national, local and mobile numbers.

Business Continuity

Delivered over a data connection SIP trunks offer a level of flexibility not offered by ISDN. Numbers can be quickly redirected, in the event of a disaster effecting your premises, at DDI level.  This allows calls to be routed directly to the correct departments, unlike ISDN services where all calls are routed to one single number.


Adding channels is quick, simple and straight forward with no site visits or physical line installations required, giving you to scale your business as it grows.

Find out more about SIP, how it works and the benefits it can offer your business.