The Government Accountability Office (GAO) has released a report on progress with the Federal Air Marshals Service (FAMS). The report can be found here:
http://www.gao.gov/new.items/d09273.pdf
The Federal Air Marshals Service operates under the Transportation Security Administration, part of Homeland Security.
There has been much speculation about what the FAMS is using for communications. The GAO report mentions some items concerning research into a viable communications solution for the Air Marshals.