Turn off radio layer hardware calls to save battery when your broadband hardware is gone
When you turn on your device, start adb shell and enter stop service rild. This would stop the RILD service and you can then use your phone for other purposes. However, on restart, the service would start again. For that, you need to edit your init.rc file. Just delete the lines that are starting the RILD service and then the RIL would not be a part of the OS anymore. Consequently, there will be no more attempts to the GSM modem.

Hope things are clear now.