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What is BT Cloud Voice SIP?


Cloud Voice SIP provides Voice over IP (VoIP) directly to an IP PBX. It can even convert a traditional ISDN PBX to VoIP via a BT SIP gateway. This single service is ideal for businesses with a mix of office-based employees using their PBX, and field-based employees who require services hosted in the cloud. By using Cloud Voice SIP, you give all your employees full access to the features of your phone system, whether they’re in the office or working remotely.


With Cloud Voice SIP, you can manage all your calls over a single data connection. It keeps costs down because calls are generally cheaper, and you can use your existing phone system and handsets. You’ll also save on line rental, because you can have multiple phone numbers on a single line. Plus it allows all customer sites and employees to be on the same Call sharer plan, as well as providing a potential seamless migration path to a purely cloud-based solution in the future.


If your business is growing, it’s easy to scale your phone system. And if you need to move premises, you don’t need to change your phone numbers because they aren't tied to the local exchange.


Cloud Voice SIP Hybrid solution offers a mixture of Cloud Voice phones, IP Telephone systems and SIP Gateways. This allows you to set up a new office without spending a fortune on hardware. The online business portals and call management system lets you manage your SIP trunks easily.


We can install a complete solution of SIP trunks and a telephone system, backed up by a dedicated customer helpdesk and support team.


What are channels and trunks?


A channel is equivalent to a phone line. Each channel can be used to make one inbound or outbound call. So the more channels you buy, the more calls you can make simultaneously. 


The trunk is the connection between your phone system and the internet, and hosts the channels you’ve purchased. Because you no longer need separate phone lines, SIP trunking can save you money and help maximise your data network investment.


How can I identify if I’m using Cloud Voice SIP trunks?


We support and maintain a range of market-leading IP PBXs which are fully compatible with Cloud Voice SIP. The following diagram shows how a BT PBX will connect to your LAN. SIP traffic routes over your LAN and uses the default gateway to route call traffic to the Cloud Voice platform.




We supply and maintain the following IP PBXs which connect to your LAN using that method:


Avaya: Version:
Avaya BCM 450 Release 6
Avaya BCM 50 Release 6
Avaya IP Office 500 V7 - V11
Avaya IP Office Connect V9 - V11
Avaya IP Office server edition V9 - V11


Cisco: Version:
Cisco UC Manager 6 with Cube

Release 6.1.1000

Cisco UC Manager 7 with Cube Release
Cisco UC Manager 8 with Cube Release


Mitel: Version:
Mitel MN3300

Version 4.2 - V7.0

Mitel MN3300 with MBG
Mitel MiCloud V8
Mitel MiVoice V5 - V8


If your PBX isn't listed in the table, Cloud Voice SIP introduces a new SIP Gateway which will support legacy or non-BT maintained PBX's with either BRI (Basic Rate interface) or PRI (Primary Rate Interface) enabling customers to use their existing PBXs with the Cloud Voice SIP Trunk service.


Cloud Voice SIP Gateway using a PBX BRI or PRI interface:



Cloud Voice SIP Gateway using a Session Border Controller:

Cloud Voice SIP Gateway using a Session Border ControllerCloud Voice SIP Gateway using a Session Border Controller

More information on BT SIP Trunks:

SIP trunking explained and how it can benefit your business
What is BT-NET?
BT Cloud-based VoIP Phone systems
On-premises phone systems
BT One Phone