It seems it is possible using blue tooth and SIP on a Nook Color that has been rooted and has the latest CM7 Nightly for Encore flashed to it. It seems that the Nook Color, like most devices that have a WiFi chip built into it, also has bluetooth capabilities built into that same chip and is only turned off at the software level. And with a community like ours, you knew it was only a matter of time before someone found a way to exploit it and turn that sucker on for our listening pleasure.
Team Douche member and CM dev Kmobs also tweeted the following today:
The nook color guys are incredible. You can now place calls using a BT headset on the nook color running CM7 with a SIP account.
I can confirm that indeed bluetooth is working in the latest nightly, I have not tried to make a phone call as of yet as I am still playing around with that idea, but I was able to turn bluetooth on, connect my wireless headset and get music playing, at least for a few seconds. The functionality is still early stage for sure, but what a great step forward. Who needs a Xoom when I have a Nook Color!