Ok, so when I first read the headline on this, I was like "WTF? How can they get away with that?"
Then looking into it - they're having problems with a small number of people (a few thousand isn't that many when you're as big as Sprint) that are calling their customer service on average at least twice a day, to repeatedly ask for information from other customers' accounts.
Honestly, it sounds like those "customers" are trying to do something fishy, and if it was my company, I'd probably do the same thing. Good call.