one option you could also try (for non video collaboration- I've done it once) is Jam Kazam.. it allows people to meet in a virtual studio online and jam.. you just need a decent internet connection, and a decent audio interface to connect your instrument to the computer.. you have a "private studio" that you can collaborate..although they try to encourage you to join jam rooms by genre....
Other wise for video Skype,Face Time,etc works well..
Skype can be audio only, doesn't have to be video. That's what I like to do so I don't have to put makeup on.
I've been co-writing, many dozens of songs, for quite a few years now. Not once has it been in person, it's all been email, phone calls, occasional audio Skype sessions (even 3-way convos). My co-writers are from all over the USA (I'm in Philly) as well as Canada, Australia, Europe, and New Zealand.
Most of these co-writers are people I met through Taxi--- the forum, rallies, Facebook, etc. And I'd say 90% of my most successful songs (in terms of getting them into really good libraries) have been these co-writes.