SIP Trunking

Connect your PBX to the PSTN in minutes with Callroute SIP Trunking

Why choose Callroute SIP Trunking

Callroute SIP trunking enables agility for your PSTN telephony. With the 2025 UK PSTN switch off looming, many businesses are being forced to explore the adoption of SIP trunking, and with services like Microsoft Teams rapidly gaining traction in the enterprise telephony space, businesses are facing a confusing array of options.

SIP trunking is commonly used for the connection of PBXs to the PSTN, replacing traditional ISDN or analogue lines. The Callroute SIP Trunking difference is it paves the way for easy migration to the cloud when your business is ready. In just a few clicks you can migrate numbers and users away from your PBX to services like Microsoft Teams, and all at a pace of your choosing using our self-service portal. 

By porting your telephone numbers to Callroute you’ll have the agility to connect them to the telephony environment of your choice in minutes. Never worry about porting your numbers again.

Flexible Pricing

Pay as you go month-to-month with 30 day notice or fixed annual commitments

Inclusive Minutes

300 minutes to UK domestic and mobile numbers per channel per month included as standard

Auto Scaling

Scale your phone channels in line with demand up to double your committed channel capacity

Migrate to Teams

Easily migrate users from your PBX to Microsoft Teams and create hybrid environments


Get immediate insights into how your telephony is performing with reporting and analytics.

Security by Default

Secure, encrypted voice traffic by default using our standard SIP TLS and SRTP trunks.

SIP Trunking FAQs

What is SIP Trunking?

SIP Trunking replaces the traditional phone line (ISDN or analogue) and typically uses the internet to connect your on-premises phone system (eg PBX) to the PSTN.

What is the UK PSTN switch off?

In 2017 Openreach announced that they are turning off the old analogue based PSTN in 2025. PSTN telephone lines include ISDN which many businesses have, these could be ISDN2 (BRI) or ISDN30 (PRI). Additional information can be found on BT’s website

How is Callroute’s SIP Trunking solution different from others?

We offer pooled capacity across trunk locations and a unique self-service portal to allow easy migration away from traditional PBX environments to services like Microsoft Teams in just a few clicks. Enabling agility is our speciality.

How many phone lines do I get with a SIP Trunk?

There is no maximum number of phone lines (channels) per SIP Trunk, you can have as many as you like. There is, however, a minimum count of 5 channels per deployment.

How many phone numbers can I get with a SIP Trunk?

There is no maximum number of phone numbers. Port or buy as many phone numbers as you need. 

Are there any setup costs for a SIP Trunk?

There are no set-up costs for SIP Trunks as our platform is self-service. However, there may be costs associated with number porting (if required).

* Moving to UCaaS platforms will change the pricing model from per channel to per active voice user

Intermittent Microsoft Teams calling issues reported globally. This issue appears to be affecting all Microsoft customers worldwide. Microsoft are currently investigating the issue. All Callroute systems are fully operational. More information will be provided as soon as possible.