My post from a similar thread here. Same issue most are having?
@seangingras; iPhone 4? I've had this issue with my new 4s, actually 2 4s's (1st one was replaced due to water damage). No apparent problem w/incoming calls. On outgoing calls I don't get sound through the earpice and toggling between between speaker & iPhone doesn't help during the call. But, once an incoming call comes in it works again for a while.
Here are a couple of trouble shooting steps I've taken:
1) from iPhone call my home phone - result home phone rings, but I don't hear it in the iPhone earpiece. Toggle to speaker; hear it through speaker; toggle back to iPhone, no sound through earpiece.
2) Call iPhone from home phone. iPhone rings, I pick up and the earpiece works.Hang up from that call; use iPhone to call home phone and the earpiece on the iPhone now works. Apparently the incoming call did something?
3) The condition from step 1) re-appears occasionally, maybe after de-activating my BT headset? Once I get an incoming call all is good for a while.
I'm following this thread and it's still unclear to me whther it is a HW or SW problem. The reason I asked my first question to @seangingras is if it's a 4, maybe it is iOS5? Given the apparent volume of this issue I've got to believe that Apple will make a statement and a fix in the near future.