A designer's rendering of the iPhone 5.
T-Mobile will start offering the iPhone 5 on April 12.
The company is currently the only major U.S. carrier not to offer Apple's popular smartphone. At an event in New York on Tuesday, CEO John Legere said the lack of an iPhone "was such a huge void in our device portfolio.''
T-Mobile is charging $100 up front, then another $20 per month for two years, on top of the service fees for voice, text and data that start at $50 per month cheaper than others.
Customers could leave T-Mobile during that time, but would still have to pay the installments.
T-Mobile's network has, until recently, not been able to offer high-speed data service to iPhones.
It's now able to offer high-speed data to iPhones in some cities.