Sounds like either there is something interfering with operation of the power-control pin of the modem shield, or (unlikely) a power-down command is being sent to the shield.Have you used the (modem's) power-control pin for some other purpose on the Arduino board?Then, if you set that 'other' state - the modem thinks you are telling it to turn off... !
Key - This is the power on/off control for the module. Its also tied to the button in the top left
Hi,What is your battery?Do you have a DMM to measure some voltages?Thanks.. Tom..
You should contact Adafruit customer service. They will swap your FONA out for a new one if they can't tell you what is wrong. The FONA absolutely needs the battery. It will not work without it. And in my experience it needs both the battery and external power supply. I run them with both with amazingly reliable results.