There wasn't even a maximum on the contract. When I got my first two phones, I agreed to a 2-year cellular contract. If I closed my account or moved providers before that, I had to pay AT&T some amount of money to kill the contract. After those two years were up, I could do whatever I wanted. I was then on a month-to-month payment, like standard cell plans today. They just wanted to make sure to recoup their money over 2 years for subsidizing my cheaper phone upfront.

Now, the subsidization is more like a subscription fee, where there are additional fees on the bill each month toward the phone and the cell phone company encourages you to get a new one once it's paid off. You're still paying full price for a phone. Possibly forever.