I'd call it reasonable, especially since there are so many stupid people leaving classified info in taxies, on unsecured laptops, and other things. Plus the Feds probably want to be able to get better access to the networks without having to go through Chinese companies to do it.

Maybe they are thinking about what happened during the Greek Olympics:

http://www.spectrum.ieee.org/print/5280

and fear it being done wholesale.

Cellphone are not secure in the first place. Cellphone signal are broadcast thru the tower, anyone could eavesdrop to the signal.

A lot easier than building a backdoor.

Politicians use Gmail accounts and other personal services to get around laws. Why would military officials be any different?

I do think it's being slightly paranoid, but I also think there's certainly the possibility of people slipping up here and there. The problem is not the paranoia, but the cover up and defense of the people who refuse to follow laws.