Original post by: Jacob Carrillo ,
It's definitely in your handset. Either someone pulled a prank and put tape or something over the receiver (I've responded to way to many calls where the user was pranked) or the receiver has broke lose which requires replacement. If replacement isn't an option you can open up the handset, find where it's broken and solder it back together. Any handset will work if it's a corded, if it's cordless you'll have to purchase a whole new base/handset or an identical handset. Good luck!