GPS and GSM interface for remote TCp server

        // Wait for '>'
        while(Serial.read() != '>');

Once again you are failing to take the opportunity to print the message coming from the device, so you are missing what the device might be telling you, in terms of what is wrong.

You REALLY need a Mega for this project, so you can have 2 external serial devices connected and still be able to use Serial for debugging.