Problems with earpiece when making call iPhone 3G

hi all,
For some reason today Im suddenly having problems with my iphone 3Gs earpiece.
When I make a call the other persons voice is distorted and I cant hear a word, just robotic crackly sounds (hope that makes some sense!) also I go to put it on loudspeaker and I get no sound at all.
Music plays fine through the speaker and is normal, and through the headphone jack no issues there.
Does anyone have any ideas?
thanks a lot
xGem
Iphone 3G Mac OS X (10.5.3)