You can be sure the Feds have already done this. 16 FPGAs, 2T of solid-state storage, and 30 seconds to crack the key on a conversation? Hell, I could probably fund that out of my own pocket.
Not like anyone with any brains didn't expect this someday. Dunno if the hobbyist crowd has done it with IS-95 or IS-2000 CDMA yet, but again, we can be pretty confident the Feds have.