(1) Almost all the handset have accessible serial interface needed for programming handsets. Moreover handset having accessible serial interface could be purchased/used.(even old ones will also do since other features are of no use)

(2) It is RS-232 only (data communi format & protocol) but just RS-232 drivers are not provided on handset. If they are using it with 8051 then there is no use of putting RS-232 drivers but otherwise I sugg them to put MAX-232.

(3) I have complete SMS AT command set that i am sending shortly