You need to move the Window Unit
In order to work correctly, the Window Unit must be placed in an area where there is 3G coverage.
To help with placement you can:
Look for 3G bars on your handset and make sure you place the Window Unit in an area with signal.
Make sure that the Window Unit has not been placed very close to a 3G router or other Wi-Fi device.
If you have placed the unit in an area where your headset has bars and waited for more than 30 minutes but the light is still flashing green, please visit http://cel-fi.com/warranty/exchange