[Boogieman]

“How tough would it be to access phone history and records from the carrier...if you know the number?”

Depends on who you are. If you’re FBI, NSA, CIA, you could access it instantaneously because the phone companies have provided you with backdoors you can access without a warrant.

If you are a member of Congress, you’ll need to issue a subpoena and possibly fight a legal battle if the phone companies are so inclined.

[Bloody Sam Roberts]

There are ways to intercept calls from specific cell phones. I've done it in the past for fun. A Simple ESN reader with some enhanced functions could do it easily.

This is one type I used to use that had audio intercept functions.