Interfacing Sim900A GSM Module with Arduino Mega R3

connection details
rx of gsm tx0 of mega
tx of gsm rx0 of mega
powering th gsm module 12v 2amps supply, connecting network , working fine.

code details:
char phone_no[]="9*********";
void setup() {
serial.begin(9600);
delay(2000);
serial.println("at");
serial.print("atd");
serial.print(phone_no);
serial.println(";");
delay(30000);
serial.println("ath");
}

but not make call.
help needed asap.
thanks , regards.

try listening (by looking @ serial.available() , serial.read() ) if acknowledge or error module. first @ should return ok.

for should move gsm comm tx/rx1 (wires , change code) , free tx/rx print diagnostic on serialmonitor.

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