To get into the programming menu, from the call screen, enter ##PROGRAM and press send. Enter code 000000.
In option 04, you can change the vocode option to EVRC-B, or 13K, it made my in-call audio sound better. I'm currently using the 13K setting. Your phone will reset after you exit and apply the new setting.
Warning: Be careful what options you change in the programming menu, you could potentially brick your phone.
Edit: Forgot to give the code of 000000 to enter at activation screen.
^^from the tips tricks and easter eggs..
I would post the link, but I don't think I have enough posts yet..
Try that..don't know if it will help though..