Hi Pramod
Just want to know, are you writing the message after module responds with ">" ? If no, then make sure you do so. This sign will come after you type AT+CMGS="9989398787" <CR> and it is recommended to type the message after module sends ">".
Well, this doesn't seem to be a reason for your problem, but make sure you do it this way. Did you check for your mobile phone settings? maybe some changes are required.