Same here with iPhone 4 w/ iOS 4.1
I am having the same problem.
Closing all apps with double tap etc didn't help.
Turning off wireless didn't help.
Cycling phone off and back on doesn't help.
Turning off push notifications and location services etc didn't help.
I don't have the answer, but would love to know what is wrong. My guess is the phone os software version 4.1 is bugged and goes into an infinite loop causing the processor to smoke the battery for some reason that doesn't affect everyone. Would love to hook up a debugger to get to the root of this as my phone is pretty useless at this point having to be charged multiple times per day.
I just upgraded to iphone 4 from 3g two days ago and noticed that it would sometimes get intensely hot. The areas that would get hot are the lower right hand side of the phone, especially the metal antenna part. I've had other cell phones and the 3g for about 15 years so I am used to warmness and a little hotness, but not like this! The temperature was such that I could fry a very small egg on the phone.
I googled the problem and couldn't really find much to resolve this problem other than returning it.
I tried isolating the problem and I noticed that this would happen only when I am in my car. I work a lot so I'm either at home, in my car, or sitting in my office. It's November here in the metro DC area, so it's getting pretty cold (hit 37F last nite), so I can safely rule out external elements.
So "room" temperatures being pretty even in all 3 environments (car, home, office), I could only think of one thing that I didn't have in my car that I had at home or in the office:
wifi. In my car I use google maps or Mapquest occasionally (with location services on) to check the traffic. Also I was using last.fm, which uses your 3G or wifi connection to stream music to your phone, much like pandora. It was when these apps were running, either in the background or in the "fore"ground(??) that the phone would get extremely hot.
I felt like I was onto something so I turned off wifi when I got home and used the 3G connection to access last.fm and check some e-mail. Sure enough the phone was cooking, very hot to the touch. I didn't want to kill the battery (heat is like kryptonite to li-ion), so I stopped my experiment before the phone got too hot and let it cool off, which it did almost immediately.
I turned wifi back on and performed the same tasks. The phone was cool to the touch. I tried using Air Video (stream videos from PC to iphone) and the phone stayed cool. I threw everything I had at the phone and it barely got warm.
So in my limited experience, I think the culprit must be the 3G circuitry. If this is a problem that can be fixed via software updates, great, but may be a hardware problem. Has anyone experienced the same?? Any thoughts?
Also, those who got replacement phones from Apple, have you had any heat related problems afterwards??