The charges against Mr Gross are to do with Cuba's state security. Jimmy Carter--as trustworthy a president as the US has ever had the wisdom to elect--visited with Gross about 6 months back. At the same time he met with Castro. There seems to be allegations of let's say 'the darker side of clandestine affairs' at work. But, who knows. Gross is Jewish, and whether or not he was distributing phones to the Cuban Jewish community or not, there has never been any love lost between Castro and the Jews. {Possibly the US got caught doing shit it shouldn't--one of those organizations with three letters in it's acronym, but, who knows. The recent requests for his release are based on humanitarian grounds (two of his family have cancer).

In short, I don't know.