Compared with other development methodologies, agile does not cause additional difficulties for teams spread across multiple geographic locations, according to Scott Ambler, writing for Dr. Dobb's Journal. Finding a good way to continue having the daily meeting required by all agile development teams is essential, however, as is a willingness to make at least some outlay on travel for team members.
I realize how difficult it can be to get a travel budget, but I've literally seen organizations waste millions of dollars on IT projects because they refused to spend $40,000 on travel. Nevertheless, it's important to realize that the development process is inherently more difficult when it has to take place at long distance. While agile doesn't impose additional problems, it doesn't remove the ones that are already there.
Teams may want to come up with a dedicated channel of communication if they must work at a distance from each other. A solution that allows the sharing of critical data like integration test results could be a lifesaver.