I scoured the Internet for a fix, and I've found a few hints that narrowed my problem down.
SYMPTOMS (With Microphone, Ear Buds, or Bluetooth):
I call and callers can't hear me.
In/Out calls work for a few seconds, then callers can't hear me all of a sudden.
All other applications that use the iPhone microphone work, yet phone app on does not.
HINTS FROM INTERNET:
Loose back glass screws.
Put pressuse on left or right bottom corners of iPhone 4.
While testing (facing the back glass), I made calls and put pressure on the left and right sides of the bottom of the iPhone 4. Sure enough, not one could hear me unless I pressed the right bottom of the ihone 4. Once I let go, they can't hear me again. Putting pressure back on, they can hear me.
FIX (So Far):
I unscrewed the bottom two screws and removed the back glass. I pre-cut a piece of manila folder about one square inch, and layed it inside the back bottom right, and put the back glass back on. My theory is that the piece of manila folder put just enough pressure on the internal components so that I did not have to manually do it.
DISCLAIMER: This is just my fix. I, nor this forum, take any resposibility for damages to your iPhone if you attempt this process.