Trouble Interfacing Sim 300 Gsm Module

HI,
i am working on a project wherein as a task i need to interface the SIM 300 GSM module with my PIC16f877a controller. till now i have been able to get the other components working which includes IR sensors, internal memory and BCD display and the USART communication. MPlab is the environment i have chosen.
The problem is
1)Whenever i pass the AT command to the modem it doesnt reply with the 'OK'.?

2) and do i need to check any particular pin (/hardware flag) or will checking OK as a string do the trick?

i have checked the hardware configuration it seems to be working fine as by communicating through the HYPERterminal software of windows the modem works just fine.
the baud rate 9600.
if theres a code kindly mail to me at f16enthusiast@gmail.com

Are you sending CR/LF at the end of your AT command?.

I m doing project on ARM Microcontroller.I want to interface Microcontroller with sim 300 GSM/GPRS modem ,please help me.