@ktasapple - this doesn't work for me...
Pressing "Use you Apple ID for iMessage" brings up a screen showing my (wrong) apple id and a password box, but then another box floats over top of that screen immedaitely prompting for a password only for the (wrong) apple id (apple id is not editable).
There's no where to sign out of imessage > I think Apple is taking this "Infinite Loop" thing a little too far.
Thank you to whomever suggested turning off iMessage (and Facetime) in Settings, then powering down. Upon powering back up and enabling iMessage I was able to fix my wrong Apple id. (same for Facetime)
Message was edited by: Cebby66