salam alikom
could you please specify what is the mobile that u are going to connect the microcontroller to
if the mobile is motorolla C168 it deal with 3.3v in this case you do not needs that RS232
by the way RS232 is used to interface the microcontoller with PC because the PC serial port deals with high and low as - 8 + 8 or -10 +10 not 0 and 5 so we need an IC such as MAX232 to convert the voltage level
salam alikom
