My phone (lumia 800) thinks all the time that I have headphones plugged in no mater if it is true or not. And when I connect normal headphones, that worked before the issue started, it opens Tellme (voice control). I've already tried hard restart but it didn't fix the problem.
Welcome to the Forum.
I would advise you to visit your local Nokia care to get the phone checked. If it needs a repair, it could be done there.