I don't know, kind of an odd problem.. I can't seem to get silent mode off. I went to Settings > Sounds > Volume > Ringer and i can adjust it, but silent mode wont turn off. The mp3 player still works but ringtones dont.
If you haven't already tried restoring your phone setting to the default I would. My friend has the same problem with the Upd=stage. It was a specific ringtone that the phone didnt like. So if you recently downloaded a non-Sprint ringtone, that could somehow be causing an error with the phone, even if it isnt assigned to anything. It could also be a 3rd party program as well. If the reset (which is under security) doesn't fix the problem, I would take it into a service center if you havent already. Oh and make sure you just reset the phone setting to factory default and not the whole phone. You don't want to erase everything on your phone. Good luck. ~SprintGod