It's basically (the older Samsung models) a Stingray detector, plus will shut down the device if activity is detected in the baseband CPU while the application CPU is dormant meaning shenanigans like SMS 'stealth' spamming is going on or evil OTA update.

You can always walk around with a portable hotspot and leave the phone on airplane mode. Only use textsecure/signal and download a free software reversed clone of Google services app to use GCM. If going to all this trouble to avoid targeted spying probably easier to just buy a chromebook with RockChip instead and use OTR or Signal whenever it comes out with desktop client (if not already, I haven't kept up with their current status of porting).