This instructable shows how to make a folding guitar. The technique of folding the neck using a hinge to the body end of the neck is not new, but this guide shows a DIY version. This guide has some interesting ideas, but I would say its still in the development stage: I can't see a mechanism to lock the unfolded neck in place. There is also a strange cylinder mechanism on the back of the neck that coils up the strings when the neck is folded, but it looks like it would get in the way when you are trying to play the guitar.

Link: Budget folding guitar