Can I connect an Arduino GSM Shield directly to a PC?
You can connect a https://www.arduino.cc/en/Main/ArduinoGSMShield to your computer with a USB-TTL serial cable, but you need to make sure you supply enough 700-1000ma to drive the GSM when it is transmitting.


  Power
  It is recommended that the board be powered with an external power supply that can provide between 700mA and 1000mA. Powering an Arduino and the GSM shield from a USB connection is not recommended, as USB cannot provide the required current for when the modem is in heavy use.