go into the phone and dial ##PROGRAM, then go to Vocode and choose EVRC-B, then hit back until you're back in the menu and choose data rates. Select the first option in the submenu and scroll all the way down to the last option. It should be one hundred fifty something by one hundred fifty something. Go back to the homescreen and your phone will automatically reboot.
I think this should help with your call quality on the other end.
EDIT: after dialing ##PROGRAM, enter 000000 (six zeroes) for the SPC password.
What does the data rate change do? And what is data rate?