I purchased my first Apple product (iPhone 4) 3 weeks ago with firmware 4.1. Finally I decided to upgrade to 4.2.1. Now when making a call I can't hear a tone or anyone talking to me. Switching to speaker works fine and so do the earbuds when connected. I read many have had the same issue and they just plugged/unplugged their earbuds a few times. Seems the iPhone forgets that the earbuds were unplugged. I tried the same and it didn't help. There is nothing stuck in the jack either. Now what?
I'll lay odds there's a piece of lint or something stuck in the headphone jack. Take a look and try to get it out with a pin or something. Happens occasionally, pretty much always to men as opposed to women. Mainly because we tend to carry our phones in our pants pockets instead of a purse.