We get the following response from the GSM modem when it initiates the call
If no dial tone we get
“NO DIALTONE”
If busy
“BUSY”
If a connection cannot be established
“NO CARRIER”
If connection successful and voice call
“OK”
so when the user receives the call (i.e. he accepts the call), we get “OK” from the modem. write tho code in such a way that once the micrcontroller receives “OK” from the modem, the audio starts.