Over the past six months, I have been increasingly using audio conferencing among two groups of 6 or more that I am part of. I have found it very efficient to keep things moving by doing weekly phone calls that everyone in the group is expected to join in. We use Asterisk, which is an open-source software, installed in my office for it, so the incremental cost for us is close to zero.
At some point of time, doing things only over email or travelling to different cities for face-to-face meetings become hard to do — especially for diverse groups. A phone call gets everyone together – and gets them talking. That, combined with the discipline of a fixed time every week, can make groups that bit more productive.