Well it seems I'm not alone in that arena as Network World has an interesting "think piece" on the subject.
With 4G via WiMax and LTE the "mobile PBX" becomes more and more a reality, as fatter wireless bandwidth makes more things possible. This is a big boon to companies who have a clear handle on the "cloud" like Skype, Gizmo, clients Truphone, ifByPhone, Junction Networks, iotum, HiDef Conferencing, wonderkind cloud developer Thomas Howe and a few others out there like Jay and Jason at Adhearsion,
Why? Because with cloud technology, and an open pipe, the mobile device becomes a smart controller, not a dumb end point. That means you can do more things from anywhere. As MIDs and Netbooks become more voice and video endpoints, not simply "data terminals" we end up with very powerful pocket and bag size devices that can do more. Client Nokia with their N900 Linux based device is heading that way, as is Apple. I fully expect Microsoft and Cisco to also be players in this evolving world of connectivity that occurs on demand, not always on all the time.