Once had a houseboat with a 2 SIM Fixed Celular Terminal on it. Worked fine. Used cordless handsets around the boat and about 500 feet ashore. Could also receice faxes and had caller ID. Used one number for incoming, the other for outgoing.

Can also be used in conjunction with your PABX to allow mobile to mobile calls through your system. If you have done a deal with you provider for free provider mobile to provider mobile calls then an FCT unit can do wonders.

Checkout eBay. I bought one resently for $45 new. Cheap and nasty Chinese unit.

Best I have come across are the old Ericsson units.