NEW YORK — T-Mobile USA on Tuesday said it will start offering the iPhone on April 12.

T-Mobile, the fourth-largest of the national U.S. phone companies, has been losing customers to the bigger companies, which all sell the iPhone.

"This is a big deal for us," T-Mobile CEO John Legere said at an event in New York.

The company will charge $100 up front for the iPhone 5, then another $20 per month for two years. That's on top of service fees for voice, text and data that start at $50 per month. The total monthly cost starts at $70 per month, a substantial discount to prices offered by bigger companies.

In areas where its network supports them, T-Mobile will also sell the older iPhone 4, for $15 down and $15 per month for two years, and the 4S for $70 plus $20 per month for two years.

T-Mobile's network has, until recently, not been able to offer high-speed data service to iPhones. It's now able to deliver high-speed data to iPhones in some cities, and it has lured more than 2.1 million off-contract AT&T iPhones, executives said Tuesday.

The new phone announcements come just days after T-Mobile ditched its conventional contract-based plans in favor of selling phones on an installment basis. It's separating the cost of the phone from the service, and when a phone is paid off, usually after two years, the monthly fee for the phone disappears from the billing statement.