This has been a post over in the Droid X forums for a while. But if you haven't already seen this, there is a way to increase call quality in our Droid 2 conversations. This site gives a very clear rundown of how to boost your call quality. Simple Droid X Hack Can Greatly Improve Call Quality | Techerator
Note i have read over in the DX forums that this is not compatible with all ROMs. But it is compatible with at least stock, Liberty, and Fission. so that covers most of us.
When you say it is not compatible with all roms do you mean that there are some roms that just simply can't access the hidden menu? Or do you mean some people can go thru all the steps but it will just not work? Or would it even mess up the call quality altogether?
This is the exact same trick the Incredible users used and the Droid users used and probably users of other phones as well. Like the article says, you're simply changing the phone to use a newer type of voice codec.
From what I've read about this, the only reason that phones don't come this way out of the box is b/c not EVERYWHERE supports this codec yet. If you happen to be in one of the few areas unlucky enough not to support this codec, just change it back if it doesn't work.
AFIAK there is no downside do making this change if this codec is supported in your area (which it most likely is). I know the article says something about faster battery drain but I don't believe the Incredible users were reporting any increased battery drain after doing this either.