MIDI is such a small format that you can easily get it in sync these days. It's very cool! With this kind of approach you can also set up an audio facility by having the other persons virtual instruments located at the same place where you are, so in that way you only need a good audio interface and a fast computer to get this technology sounding amazing. Soon there will be ways of transfering the other persons whole setup first before the jam starts.

Since audio is a much bigger format there are currently no fast enough communication methods to handle audio signals fast enough to not cause too much latency when playing live together with somebody on the other side of the world. Until then we will live in an age where MIDI and virtual instruments will lead the way. There are many interesting things that fast communication methods can do together with music in digital format. In the future you will be able to do for instance this:

1.Search for musicians that want to play a certain setup of songs together with.
2.Together choose instruments, mixer, effects, amplifiers and cabs for the gig.
3.Perform in front of an audience.
4.Store the music on DVD.
5.Sell the DVD.
6.Buy another one's produced DVD.
7.Modify the mix however you like.
8.Sample the instruments you heard on the DVD.