Even im working on the same project.. interfacing uC with a gsm mobile as a home appliance controller..at commands being the basic accesing commands..im currently working with a nokia 2100..i bought a connecting wire which goes in the slot under the battery of 2100(even a 3315 has slot under the battery which you must have observed) and the other end being a db9 connector going to the com port of the computer for testing purpose which can later be interfaced to a uC..RS232 MAX 232 driver nd stuff..i hav been trying to access the mobile by sending at commands thru the hyper terminal program in windows with no success..not sure why..the baud was set to 19200,data bits 8, parity none, stop bits 1, flow control hardware or none. these were standard values which i found on the net..