Arduino GSM shield GSM_READY not ready ever
You could always try setting a pin code and then retry
http://arduino.cc/en/Tutorial/GSMToolsPinManagement

What version of the Arduino IDE are you using ? Also, are you sure you are suppying the board correctly ? "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."