Send/receive MMS/SMS by GPRS communication in c#

Hi everybody!
I’m working project about sending and receiving MMS/SMS message by GPRS communication from PC through GSM modem.
But I dont know what commands is used for this sending/receiving.
Please help me some source code(in c#) for " send_message; receive_message "!
And : please reply for me as soon cause My time still not much!
Thanks !