Problem with Samsung D840

Hi I have been using my Samsung D840 for some time now with out any
problems now I have the following problems. When I dial a number I can
not hear it dialing, I can not hear the person when they answer and
they can not hear me. Every thing else on the phone works as it
should.
Any idea as to what may have gone wrong and what needs to be set or
reset to cure the problem.
Thanks
Tony