So maybe one of you can help me out with this strange issue I'm having with my iPhone 4.

Few backs I started to notice my phone would crackle when I made or received calls. Jump forward a few weeks and now I can't even hear anything! No dial tone, no voice, no crackle (though the phone is connecting the call).
Here's the strange bit though. Music plays fine, I can talk, record and playback voice notes perfectly, and I can listen to my voice-mail in perfect clarity. It's only when I make and receive calls does it get all messed up. I've tried speaker phone and still nothing.
It gets even stranger. If I press on certain parts on the back of the phone, I can hear the calls.

Anyone ever experience this, know what I'm talking about, or have a solution or inclination as to what it may be?

iPhone 4 running 4.3.3, jailbroken of course.