My new iPhone 5 (I preordered mine from AT&T on the morning of the 14th and received it on the 21st, so I might have one from one of the earlier batches) likes to heat up intermittently.
I've noticed a general correlation between the cellular connection display showing "4G" and when it tends to heat up by itself. It seems generally capable of heating up to a temperature higher than it would get to from just being in my pocket, and just to be sure I have left it on a table and observed the same effect.
What's curious to me is that whenever the display shows "LTE" this effect is not as pronounced. When I'm at home I usually see LTE but at work it spends a good half of its time in "4G" mode and this warms it up and sucks the juice out of it real quick. The data connection is definitely faster on LTE mode also.
All of this seems to indicate some sort of software bug with the 4G cellular hardware in the device, as it makes no sense why it should struggle more when connecting to what appears to be a slower network. I hope that Apple is aware of this and that it may be addressed in the near future.
Has anybody else noticed this issue with their iPhone 5? I have searched a bit on Google but it looks like everybody is pretty much too busy playing around with their new gadget to complain about (or notice) this particular issue I have. My thinking is if lots of people also experience this issue it's more likely to get addressed.
Update: I have found this page which more or less reflects what I am seeing, except my observation is that low signal "4G" causes very high power draw. If I need to make an emergency call I could justify this level of power consumption. But calls do not require high speed data connections.
I just hope I don't have to wait for the jailbreak before this becomes fixed, in fact I really doubt a jailbreak would allow me to tweak radio hardware either.