My notification sounds stopped working. Anyone know why? Been missing calls because of no sound. Speaker is fine.

My notification sounds have stopped working. Anyone know why? My speaker is working. Can choose a ringtone on iPhone 3GS and hear it but when I get a call it just vibrates. Have reset phone settings still no ring or message alerts. Didn't change any settings but did get an iPhone update yesterday. Any ideas?? Been missing messages and calls.