Credit: Stephen Yang/Bloomberg/Getty Images

This Friday is a big deal for T-Mobile. After five years, the wireless carrier will finally start selling the iPhone. But the company is also sweetening the deal for customers: From April 12 through June 16, you will be able to bring in your iPhone 4 or 4S and trade it in for credit towards the iPhone 5 so you can get the phone for no money down.

If you bring in an old iPhone 4 or 4S, you'll get the iPhone 5 with the $100 down payment waived. Plus, you'll get a credit of $120 depending on the type and condition of the iPhone brought in. The rest of the cost of the contractless phone can be paid off over the next two years at $20 a month. Or the credit can be used towards a service bill or even accessories

RELATED: T-Mobile's Contract-Free Plans Explained (Like You Don't Even Know What a Phone Contract Is)

The iPhone 5 will be offered with T-Mobile latest contract-free or Simple Choice Plan. You won't have to sign a contract on the phone - instead you pay month-to-month for your cellular bill and you can back out anytime. The plan starts at $50 and buys you unlimited voice calls, texting and 500MB of data. Adding 2GB a month costs an additional $10 and unlimited data adds $20 more.

But because you aren't signing a contract and T-Mobile isn't subsidizing the cost of the phone,you have to either pay the price of the phone upfront or over two years. In this case, the iPhone costs $99 up-front, but if you bring that iPhone 4 or iPhone 4S in T-Mobile is waving that cost. You still have to pay the monthly $20 for the cost of the phone.

Verizon, AT&T and Sprint offer the iPhone 5 for $199 but only if you sign a two-year contract, wedding you to the carrier for two years. The details on T-Mobile's no-contract pricing can be found here.

T-Mobile, which has been the smallest of the major four U.S. carriers, announced last week that it gained subscribers in the first quarter of the year, it's first such gain in years.