I was wondering how difficult would it be to disable the broadband processor on an iphone or Samsung Galaxy? Or better yet possibly install kill switches on them?
While not strictly impossible, it’s for all practical purposes impossible. The broadband processor is integrated into the main SOC, so you’d have to know the layout of the SOC and laser it off. Oh, and it would be a one-way operation, no re-enabling it later without soldering on a new SOC.
Well, seeing as how the OP never specified which Samsung Galaxy version, you could in theory do it with the Galaxy S4 and earlier, which had a separate modem chip. You’d need to locate the power lines to the modem on the circuit board, very carefully cut them and then splice in a switch (which is not an easy task). I do not know what side effects this would have, as the system was in no way designed to have a hot-pluggable modem.
Aside from that, your device would get noticeably bigger (because of the extra switch and almost certainly some circuitry to make that one switch control multiple power lines) and would be INCREDIBLY fragile (those are tiny circuit traces you’re messing with, one small drop and you’re going to break the tiny little solder joint you made).
Ithings would also be possible in the same way - Apple use separate modem chips (there were several news articles in the past about how phones with Intel modems had worse network performance than those with Qualcomm modems) and you would also face the same problems (very difficult circuit work, system was not designed to be hot-pluggable).
I appreciate the insights. Perhaps it is easier to make an on/off switch to disconnect the battery? I was thinking about doing this with an old iphone such as a 4s. I was wondering what possible consequences that would have as the iphones were not designed to be turned on and off.
That would be more doable, the new ones really aren’t designed with user access to the battery in mind, so they may or may not be resistant to corruption from having the power cut without warning. At the least, you could shut the phone down then cut the power and know that it isn’t listening anymore. Still, the routing is going to be difficult; you would want to pick a relatively low power signal trace to hijack so that you could get away with a small jumper wire.