Guys the same thing happened to me! Luckily my sound is working now, for how long is the question, I hope it works ok now all the time! Lol. I have a sneaky feeling this isn't the case though as to what I have read.
Well I updated my iPhone 4 and bam! My sound didn't work correctly. It would play my ring tone, but not my tone and the key pad clicks through the device. It would not play music, video's, or app music either through the actual device. But if I plugged the headphones in hey presto the sound would play just fine through those. Also whilst I was on the phone this would work ok, and ok on the speaker phone. My alarm would play sounds also. If I pressed the volume buttons, I just got a blank ringer with no tab's underneath.
I tried restoring it, cleaning it, nowt worked. Just woke up this morning and the sound was working again. The sound was out for at least 5 hours last night.
Sort it Apple! Clearly you are at fault here! All this money we pay for our phones and this is happening, jeez :-(