Yes and no. It depends on the area that you live in and if they have the enhanced vocoder available in that region.
But, something that I did that fixed my call quality dramatically on my old Droid and which I implemented straight away on my DX is to Settings...Call Settings....and to UNCHECK the Voice Privacy option. It always sounded like I was underwater when activated. Besides, I don't work for the NSA so what's the point?