I can be done with a bit of fiddling on Hyundai and Samsung.

Changing from default EVRC to "13k call" (samsung) or "QCELP 13k" (Curitel, Hyundai, Pantech)

Has anyone actually done it and comments on usage please.. I think it sounds FAR FAR better and make CDMA very usable, The normal Voice carrier sounds very shrill and there is no tonal syllable definition plus it blocks out background noise which it seems to block speech too much and makes any background noise into horrible sounding Electronic noises though it would be kinda cool for some music :-)