A chat and email solution is one aspect.
But we humans can convey more information via spoken language and mimics. An audio and video connection for interacting with the team member across the globe is important.
Use IM with integrated Audio and Video, and which enables desktop sharing for collaborative working.
To stitch further the sense of a team despite of the distance, you can extend the office with the view of the other offices' common room filmed from a camera onto a video wall. Of course there is a privacy issue, and not everybody is comfortable with it. It is worth a try
When do we get the connected rooms across several rooms from Dan Simmons' Hyperion???