Share 'not able to receive incoming messages'

i was doing a quick test with frontline sms using a gsm modem and was able to send a test sms to my phone ...i tried replying back to that sms from my mobile with a keyword that i had set. like 'vote1' which was never picked up by frontline sms.is there any format for the gsm phone number ?? we are planning to use this appln for a simple polling pls helpThanks,Varun