GSM signal lost - howto get signal back without restarting
The following is no complete solution, but at least a work-around, avoiding a long reboot:

There are apps like Quick Boot (others have things like "fast reboot" and the like in their names/descriptions). Other suggested by those names, they do not really reboot your device, but simply restart the system server (for details, please take a look at Can somebody explain the boot process of an Android device? – the system server is started at step 5 of 6 boot steps, so this skips more than half of the way down and up, effectively resulting in a process about 3 times as fast as a complete reboot).

While this way all your apps are killed as a side effect (as they require the system server to work), it's still a lot faster than a real reboot, and thus "less hazzle".