I just heard this from a commentator on ABC News:
[US Intelligence] has the ability to "Sweep up all communication going
around the world in a very broad way."
There are currently "millions and millions of phone calls in this vacuum
cleaner."
"They will be sorting through all of the communications going through phone
numbers that they have an interest in."
The reporter also mentioned that the officials have to be careful not to
intercept calls of US Citizens.