Well THAT might cause and overheat. though 100' does not sound unsafe Stuff it in your pocket and its gonna be 98.6 in short order.
But yeah downloading a torrent is gonna keep all the radios maxed and on 100% duty cycle. that will probably make it a bit warm. I know most of my phones are physically warm (anything that feels WARM to your sense of touch is over 98') and almost hot after a really long conversation. Especially the smaller phones (less material to act as a heat sink)
But if all it got was 100' I would not be too concerned. An idea is to leave it on its face and remove the battery cover. It will cool better and make sure the screen backlight is OFF and the screen as well if possible (less E usage less heat build up)
Torrents?? Over EVDO and sprint does not mess with you! WOW
As for phones not overheating. How many phones have you had? every single phone I have ever owned has gotten physically warm to very nearly HOT (some of them downright hot as in well over 120') after extended usage.
Far less when used with headset (no "face" to insulate and provide heat) but yeah my sanyo 6200 damn that bugger got hot enough to scorch me a little after a 30 minute conversation
Future phones same thing to differing degrees.