Today almost complete the second week with my IPhone 4 and suddenly it becomes hot at bottom-back part.
I noticed this because I had the phone in my pants' pocket.
It was hot as if you put your hand on a cup of coffe.
After about 5 minutes it went to normal.
I really don't know what is down there in the phone , but I think that is the antenna and could be RF or PA.
I'm not using any case or protector.
I've charged twice and never got hot like this during the charging time.
If someone has seen this problem please let me know.
***Edited to add labels***
Solved! Go to Solution.
mmm, It could be, I was taking a look to the map application and then I locked my phone and put it back in my pocket.
I'll continue monitoring it
Thanks for your advise