Here is a section from my program to send a sms. I'm using a WAVECOM modem, but I think the AT commans are the same for all brands.

sms:
HSerout ["AT",13]
HSERIN 5000, SMS,[WAIT("OK")] ' wait for response ok for 5 seconds
HSerout ["AT+CMGF=1",13] 'Set Text Mode
HSERIN 5000, SMS,[WAIT("OK")] ' wait for response ok for 5 seconds
HSerout ["AT+CMGS=",str tel\14,13] ' dial the phone number
HSERIN 5000 , SMS, [WAIT(">")] 'wait for a response to send the message
HSerout ["Esto es solo una prueba",13] 'write the message
HSerout [26] 'exit message mode
Pause 500
GOTO ESPERA 'exit sms rutine

and it works great!!!!!!!

I hope it can help you