I had the same problem. I didn't do anything, as far as I know, it just stopped making any sounds at all.
I've checked all my profile details, they're all set to tone... I can't figure it out!!!
Is there a general device volume thing that I'm missing?
I haven't changed any thing on the phone. I did do a battery pull, still no matter what profile I use (loud, normal, quiet, ect..) the only thing that will work is vibrate. All the others are like silent mode. very strange.....