phone muted during calls! help!!!

I have an htc desire s and when i make calls the phone is automatically muted. There is a line through the little mic symbol and it is unresponsive when i touch it. I have to turn on speaker phone to be able to talk to people and it's really annoying! any help would be great thanks!

just for giggles, fiddle with the volume keys during a call. I honestly don't know if that would have an effect, but that would be my guess