Last October, Men's Journal did a cover story on Lance Armstrong that recapped his fifth Tour de France and his life at that time. A side bar to that article called The Innovator: The Winning Gear discussed many of the components that Armstrong and the U.S. Postal Service team used in the 2003 Tour. The article says that the team uses Alinco DJ-C5T two-way radios. These credit-card sized devices are more likely to be used by ham radio enthusiasts in the United States than by athletes.
eHam.net has user reviews of the Alinoco DJ-C5, which has the same size and appearance as the DJ-C5T.
Alinoco manufacturer maintains a website, but doesn't list the DJ-C5T. I'm not sure why that is.