2G or 3G wireless would be attached to someone's account (i.e. associated with a person).Easily solvable with shills or shell corporations. Think about the options of the authorities in the US. Police would have to get a search warrant. Which address are they going to get a search warrant for? The shill/shell company might have nothing to do with the whole thing other than maintaining the 3G accounts.
The authorities could just access the contents of the drive to see what is on it. (though this would obviously mean infiltrating the darknet)
This might also mean infiltrating the organization to get access to the darknet. This would seem to indicate that the level of physical security I'm suggesting is commensurate to the task.
It would probably be easier to setup something like this hooked into the internet at some private business. Stick it under a desk or above the ceiling tiles and just plug it directly into the local network.
That's exactly what I'm thinking of! That would be another viable option for hosting such a device.