If you are subscribed to either plan, and are unable to send and receive messages:
Check communications: Check to see if green light to the left of the Home button on your device is on. This indicates the device has power. If not, verify the cable is connected to the back of the unit properly.
Restart the device: Restart the device by first logging off, then pressing the Power button to shut off the device. Once the device has been shut off, press the Power button again. This will cause the device to reset and reconnect.