Re: Callers cannot hear me talk when they call, I can hear them.
If they can hear you when you call them you probably have a firmware problem. (If the phone received an over the air update, take it to the carrier and ask them to fix it - it's their liability.)
If they can't hear you at all using the internal mic, but they can with a headset, check the mic hole. (Look in the manual to find where it is.) If there's lint or dust in it, use a pointed wooden toothpick to carefully clean the hole out.