Recent posts on the AirCommSouthwest Yahoo group were concerning the Federal Air Marshals Service and an incident involving an Air Marshal on a recent flight. After the incident, in which a passenger was subdued by an Air Marshal, the FAM requested the pilot call in a report of what happened. The pilot was heard on an ARINC VHF air-to-ground frequency calling in the incident. Some wondered about what the Air Marshals have to communicate with while on duty.
Although there have been reports of some type of satellite or world-wide communications system, the Federal Air Marshals most likely just have cell phones. One list member posted a link to this document that mentioned the TSA and Federal Air Marshals Service using satellite communications:
However, further searches on the subject of the Air Marshals Service and satellite communications reveals this story:
It seems that if they have a satellite communications system, it doesn't work as advertised.
I also received some anonymous information regarding the Federal Air Marshals and a UHF radio system that was installed for the New York Field Office:
F1 408.050 (418.050, input)
It's not known if these are used nationwide or only in the NYC area.