well i was reading up ona a thread here where it listed the best radios for different cities. I live in newyork and i am on sprint. The thread said that the verizon radio was better in new york so after i flashed to that verizon radio my phone is significantly less hotter when using voice and when using data.The sprint radio would get incredibly warm so it may depend what radio you have and where you are located. try looking up the thread on best radios for different cities(i dont remember where it was)
edit- found the thread.hope it helps.
http://forum.ppcgeeks.com/showthread.php?t=56611