Well, by far the easiest way to time travel to the future is just to go very very fast, then relativity will put you there without the need for wormholes, black holes and so on.

Of course, that's not reversible though, going very very fast backwards won't help.

Dunno about the black hole / wormhole approach, I'd thought there was no way of transmitting information across a black hole event horizon.

Worm holes might be another matter though.