I fiddled with the interface back when there was MAC 0S 9 and was successfull in modifying a modem driver. The "AT" like commands are "different" when connecting to a cellular network. Usually, your setting up a PPP like connection. They can be, in esscence, a superset of 56K modem, fax and GSM. Off the top of my head, I forget where I found the documantation.