Keep in mind, my point was that the possible trade-offs seemed worth it to me. > Is this a big deal? The device can just discard it. I read someone around her

Keep in mind, my point was that the possible trade-offs seemed worth it to me. > Is this a big deal? The device can just discard it. I read someone around here who stated this was the original goal of firewalls. The device could indeed discard it, but having dedicated hardware for that check could avoid denials of service. > I've used a SIM with a non-firewalled public IP for months. I haven't noticed any extra battery drain. I am a bit jealous: mine is firewalled. Such extra drain could happen if you had, say, an ssh server on it, and someone was trying to bruteforce its way in, or if you had an http server with a few crawlers hitting it, but those are theoretical issues. On the other hand, you get much easier push notifications (too many of those, and the battery starts being an issue again).