Is it always bad, or sometimes bad? I have the gen1 with bt, and it is intermittently bad. I think this is due to interference, if you disconnect and reconnect, the pairing should get a new channel, and hopefully it fixes it. If it is always bad, then there is a different problem. I have had the same intermittent quality problem on other bt devices as well. People say it sounds like you're under water or really far away.
Workaround:
I tell the phone to go to speaker, and then reconnect bt and it works fine.
(Technical guess - I think when the phone and bt pair, a channel is chosen, then when you drive you end up in an area that has interference on that channel, re-pairing will cause the system to pick a better channel.)