Chech out this thread, may help for those with a crappy sound quality.
http://forum.xda-developers.com/showthread.php?t=684022
Go to Phone and Dial ##778
- Choose Edit Mode
- Password is 000000
- Go to CDMA Settings
- Scroll all the way to bottom
- Change Home Page, Home Orig, and Roam Orig from EVRC to EVRC-B
- Hit Menu and Commit Changes
- Phone reboots and walla no more muffed voice calls!
- enjoy your uber phone.
edit: There is a TON of data in this mode and you can apparently change a ton of stuff too...