You can further debug the phone by communicating with the GSM module via serial communication with the computer, using the microcontroller as a proxy. To do so, upload the SerialProxy sketch to the phone (using a 3.3V FTDI cable or breakout board). Then open the serial monitor and set the baud rate to 9600 and the line ending to "carriage return". After a few seconds, you should see:READYATOKThat means the GSM is ready to receive AT commands (text strings that mostly start with the letters "AT"). The commands are detailed in the datasheet for the GSM module but here are a few basic ones:
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