Voice-only would probably be best to start off with, but my ORIGINLA VISION (TM) for this is to have video as well.
I've never done it, but I think you can record audio+video multiways with Skype.
And shame on you Gaffer, you've been spending all of your time thinking about MMPR instead of eagerly anticipating Inception.
Inception should be billed as "From the Writer/Director of the Prestige" since I think Inception will have more in common with that movie than his Batman work.