We have a team of four as well, all in different states. We LIVE inside Basecamp, which either updates projects or daily tasks automatically or through user input. Either way, you can live inside one app vs. chasing disparate emails.
We have started using "P2" which is a theme built by Automattic (Creators of Wordpress) and is used internally by them and they have hundreds of employees, all around the world. It's a great way to keep everyone connected, and is so much nicer and easier than group emails etc.
It's free! And you can find it here: http://p2theme.com