No one has ever actually managed to transfer matter - which is essentially what would be required to teleport humans around the place - this remains impossible.

Theroetically there are ways to do similar kinds of things - but these aren't ways that would work with matter on a large scale. And certainly aren't able to overcome the problems that the individual (in terms of human personality) would come across in being teleported.

Oddly enough, Star Trek never really delved into just what a mind fuck it would be.