. . . communicate, communicate, communicate! Use many different tools to reach people.
In this article, Bob Taccini, a Cisco Systems vice president, discusses his use of vlogs (video blogs), blogs, teleconferencing, videoconferencing, discussion boards and the good old fashioned telephone to communicate with his far-flung team: http://blogs.hbr.org/cs/2010/06/leading_virtual_teams_to_real.html.
You'll find a wonderful list of tips for leading virtually in the article as well.
vintage phone image: Daniel St.Pierre / FreeDigitalPhotos.net