Thanks dans. So, in order to get an internal dial tone, the user must call in with their cell phone and somehow get to their assigned mobile extension number. We aren't using DID. I suppose I could eat up an analog CO trunk and make it DIL to the mobile extension, but that seems wasteful.

Intercom calls or transferring a call to the user's deskphone, with the proper call forwarding, should call out on an idle trunk and ring the cell phone? Can you receive calls through the mobile extension number?

Thanks.
Jim