In an unprecedented move, T-Mobile will join AT&T, Sprint and Verizon to support Apple's iPhone on its network. 

The network announced on Monday that staring Sept. 12, it will be training its staff on how to set up compatible iPhones. The carrier said each of its branded retail stores will receive an iPhone demo unit.

T-Mobile said there are a lot of devices running on its network that are not sold in their stores, including more than one million iPhones

They said they are developing iOS versions of helpful T-Mobile applications likeT-Mobile myAccount, T-Mobile Visual Voicemail and T-Mobile TV. They already offer an iOS version of our popular Bobsled application.

T-Mobile said customers who bring an unlocked iPhone to any of its stores will get an unlimited data package and can save up to $50 per month compared to AT&T. The savings are based on comparison of T-Mobile $69.99/mo Unlimited Talk, Text and Data plan against AT&T Unlimited Talk, Text, and 5GB Smartphone Data plan. 

On Sept. 5, T-Mobile became the only carrier with a nationwide 4G network to offer unlimited nationwide 4G data.

"We're big believers in customer-driven innovation, and our Unlimited Nationwide 4G Data plan is the answer to customers who are frustrated by the cost, complexity and congested networks of our competitors," said Kevin McLaughlin, vice president, marketing, T-Mobile USA.  "Consumers want the freedom of unlimited 4G data. Our bold move to be the only wireless carrier to offer an Unlimited Nationwide 4G Data plan reinforces our value leadership and capitalizes on the strength of our nationwide 4G network."

Verizon and Sprint iPhones will not work on T-Mobile's network and other iPhones may have limited functionality. 

They also said internal tests of unlocked iPhone 4S devices running over 4G (HSPA+) on its 1900 network recorded on average 70 percent faster download speeds than iPhone 4S devices on AT&T's network.

T-Mobile's voice network reaches 96 percent of all Americans, and later this year, will introduce 4G (HSPA+) service in iPhone-compatible spectrum, giving unlocked iPhones a significant speed boost where these improvements are available.

The phone carrier said they have started turning up 4G HSPA+ service in its 1900 MHz spectrum and sites are already live in Seattle, Las Vegas, Washington DC and the New York metro area. 

"Today, we don't sell the iPhone, but we do have something worth selling to people who have one," Suzanne Lowry, vice president of marketing said in a release. "Our message to iPhone customers is simple: bring your unlocked iPhone to T-Mobile and save."