Inspired by this diary I did the math. (in a comment there)
It isn't just the phone numbers they are recording.
Suppose you were to record the phone calls to and from all people in the USA.
Each record is about 24 bytes. 10 + 10 + 4 for the time.
330 million people, an average of (say) thirty a day? (remember I'm counting 2 year olds in this). Think about how many calls are on your monthly statement if you get call detail.
10 billion calls a day? By 24 bytes.
240 billion bytes a day.
I HAVE 1/20 OF THAT ON THE LAPTOP I'M TYPING THIS COMMENT ON
20 hard drives a day... is that a bleeding edge database?
They aren't recording the numbers.
They are recording the calls.