Here is what you can do to improve call quality. I have done this on every customer's Droid.
##7764726 (##PROGRAM)
CALL Button
Enter SPC Password - 000000
VERIFY
04 Vocode
Select EVRC-B
This will change how the phone compresses and decompresses call audio. Seems to work really well, I have noticed and improvement for sure and I no longer get the "you sound like you're underwater" complaints from people I talk to. Give it a shot!
Are there any negatives/risks to doing this? If it is so great, why isn't it the default?
He had already stated the reason this isn't the default right now is because it's not FULLY supported on every single cell tower. While most towers support it, there may be a couple that do not, and verizon doesn't want you to not have coverage due to this small problem. For the vast majority this will NOT be a problem, though for those who switch over to the new vocode, and you no longer get signal where you are, switch it back immediately.