This used to happen to me every so often with my first 6700 (purchased 11/06.) It would typically happen in the middle of a call, leaving me to fumble around for my phone, yelling "hold on a second...my headset disconnected!" I have been through many ROMs since then, and the problem occurred with each of them.
I had my phone replaced with a refurb several weeks ago, and the problem hasn't happened since. Of course, the local corporate Sprint store had been totally unwilling to help me, even going so far as to say "you should add another line to your account, so that if this happens again, you'll have a more reliable phone to use." I had much more luck at an authorized repair center. Since they weren't authorized to repair my phone, they just filled out the forms to get me a new one (refurb.) I'll never go back to a corporate store again
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One ROM to rule them all,
One ROM to find them.
One ROM to bring them all,
And in the kitchen, bind them.