Hi,
So I'm using a SIP Voip app called Bria to connect to our mitel system which works but we want it to also share an extension with one of the Mitel IP 5324 sets.
If I try to set the extensions to be the same I get a ext already in use error.
Devices cannot "share" an extension number in the MiVB... You would create this as another device under the same user, say if the main extension is 2345, create it as 2*345 or something like that, than create a Multi-User Device Group for the main extension and add the SIP extension to that group.
There other ways to accomplish this, but this is the most common these days.