it could be a defective phone...as i feel the voice quality (on both ends) is at the least on par with my dx, the only time the dx was better was in a noisy environment, but it had 3 mics.
i would go to a verizon store, see if they can diagnose it in person.
if you're in your 30 days, have them go through phones until you find one that has good quality.
i got more echo/reverb on my dx than i do on my fascinate...