Interfacing GSM module with uC

Hi,
For one of my projects I need to have serial communication (TXD, RXD pins) through a GSM module. Can anybody please give some details on this OR suggest some sites where I can get more practical details. I am using AT89S52 uC and doing the programing in C (using KEIL). Would be very useful if I get a sample program also (does it depend on the type of GSM module I use?).

Seems to be a popular project on edaboard.