T-Mobile, having taken note of Apple’s successful App Store, plans to launch its own version in the fall, according to mocoNews.net.

The fourth largest carrier in the U.S., T-Mobile has been slow to roll out 3G and is losing customers to AT&T. In addition, noting that Apple and its developers have raked in US$30M in one month, the carrier, according to a developer knowledgeable on the matter, plans to ditch its traditional app model in favor of more open model, available on all of its phones, from Sidekick to Android, and all of its subscribers.

T-Mobile believes that its 31 million subscribers will give it momentum compared to the approximately 10 million iPhones Apple expects to sell by the end of the year.

The key will be embracing developers and bringing them onto the platform. T-mobile will have to work fast as observers noted that T-Mobile only added 668,000 net subscribers in the U.S. in Q2, and that was disappointing compared to 857,000 a year ago, also seen as low.

T-Mobile has declined to comment, but Venetia Espinoza, T-Mobile’s director of Mobile Applications and Partner Programs said, "T-Mobile is working with the industry to foster an open wireless services platform which will provide developers with the tools and information they need to make new, innovative experiences available to T-Mobile’s more than 31.5M customers. The devPartner Community site, which is in its alpha stage, is just a taste of what T-Mobile has in store and we encourage you to stay tuned for more details in the coming weeks."

T-Mobile will face several challenges in its devPartner program. Apple already has a significant head start, a strong Unix platform with OpenGL type graphics, a lot of sex appeal in the iPhone, an experienced and enthusiastic developer community and a strong partner in AT&T. However, no mater what the outcome of T-Mobile’s efforts, Apple’s model appears to have set the stage for a whole new approach to software on smartphones.