In the past they sidestepped the law about spying on their own citizens by partnering with other nations, then swapping lists of people to monitor.
This was ECHELON. There were 5 nations involved: The US, Canada, the UK, Australia, and New Zealand.
(http://en.wikipedia.org/wiki/ECHELON)
That was before 9/11. Why are people surprised that warrantless wire-tapping happens now?