I have sprint pcs and a samsung A640.

Be careful if you adjust any of the hidden settings...I figured i would, and ended up going back to factory default settings, with just a +1 adjustment to one of the volume settings. I had done some trial and error, thought i had it good, and repeadly, when i made an outgoing call, most people would just hang up on me, saying there was too much noise on the line to even begin to carry on a conversation.

Guess my trail and error procedue was flawed...at any rate, it is first rate now....