i have a similar project(Send sms  From Web
appplication)....
in this applications u should create a sms packet and
send it to sms server...
your packet is customiz by sms server so sms pcket
strutcture changed by one sms server to others...
you should ask from how's that impelements your
GSM&Smpp Protocols....
otherwise! in your program you should only create a
CUSTOMIZED packet structure and write it to the
Spesifeid Address(Socket Address:IP,Port Number)