Sometimes, a forum or even a chat is not enough. You want direct communication with someone across the world, with voice and visual support. For quite some time now Skype is one of the leading Voice-over-IP solutions, even having support for connecting to the outside world (=regular phones) and creating phone conferences (=phoning with multiple people).

Add a nice screen-sharing program to that, maybe even a collection of web-based productivity applications and you should be able to discuss and write down your ideas pretty quickly.