Arduino and modem tel0124 not sending at in serial monitor

Can anybody help me

i trying to sent AT commands to thr Tel0124 modem via the Arduino serial monitor. 
i can send a sms though a program, but would like to send at commands via the serial monitor to get the correct code sequence for connection to a sql server using a php model. 
even when i write just AT  in monitor nothing comes back. 
What di i need to do to be able to write at commands in monitor