Now you got all. The freted/fretless stay on 1 bass. 
http://www.youtube.com/watch?v=vB7c3OsZHNE&feature=related

http://www.youtube.com/watch?v=vB7c3OsZHNE&feature=related
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It has been posted many times before. I don't remember the name of the brand. But I remember that it was really expensive.
More expensive than a nice fretted and fretless bass. Unfortunately, it's not a terribly feasible concept as you end up with a fretless with high action.
LOL, this and Stig's headstock bass DESERVE a sticky.
wouldn't the intonation be kinda screwed too?