They don't have the legal means to do it, but anyone who thinks they won't when the mood strikes, is out of his mind.
Somewhere on the net, there is a copy of all of the text messages sent the morning of 9/11/01 that came out of the investigations of that day.
How much better do you think their vacuuming is today?
One thing that's funny about this is that during actual disasters, (Katrina comes to mind), it's not the government who has comms in the disaster area. It's the Hams.