In the film, the protagonists decided to get back at their evil employer by running some software on the company servers that would round down all the transactions to the nearest cent and then dump all those fractions of a penny into a new account. The premise is that no one would notice those fractions but over millions of transactions it would add up to some serious cash. 

That's exactly what AT&T is doing to customers. By adding a $0.61 administrative fee to each customer every month. While it might not amount to much per customer, it amounts to half a billion dollars per year when you add it all up. 

By locking customers into two-year contracts, they guarantee that those customers can't leave.  The "downside" from AT&T's perspective is that they can't just raise their prices because the customers are under "contract." Instead they just create a new administrative fee that looks like a government charge. Nice if you can get away with it, which only big corporations like AT&T can do.