Same thing happened to me. One day the speaker just up and stopped working. Removed and reinserted the battery...wiped handheld and reloaded handheld software (made a backup first hehe) With none of my data on, still no speaker. Found my box and recipt...took it back to the tmo store i got it from. Exchanged it for another one.
I hope this isnt a known issue with the bb...well i kind of do that way it can be resolved by rim and then handled by tmo.
Quick question though: Was yours ever dropped? I know i dropped mine once on some carpet and the fall wasnt very far.