Just yesterday we heard rumors from the Wall Street Journal that Sprint would be carrying the iPhone 4 and iPhone 5 at launch, marking the first time that the nation’s third largest carrier would be offering Apple’s smartphone.

Now, rumors are surfacing that T-Mobile will be carrying the iPhone 5 as well, and that it will run on T-Mobile’s 3G network, reports Mactrast. A source inside T-Mobile has informed the site that T-Mobile will be offering the iPhone 5 alongside Sprint, Verizon and AT&T in early to mid October.

The anonymous source claims to have been ‘briefed’ on the launch and that the iPhone 5 will indeed support T-Mobile’s 3G network, which operates on the 1700 MHz spectrum, while AT&T, and the iPhone, runs the 1800 MHz spectrum. This prevents current unlocked iPhone 4 users from utilizing T-Mobile’s 3G speeds, limiting them to the 2G ‘EDGE’ netowrk.

The source was optimistic about the iPhone coming to T-Mobile, stating “We expect the addition of the iPhone, and the iPhone 5′s ability to run on our 3G network to make a significant financial difference for T-Mobile.”

Now this whole rumor smacks somewhat of wish fulfillment for T-Mobile users, who had long expected the iPhone to come to their network first, as it is a GSM carrier just like Apple’s preferred launch partner AT&T. But that didn’t happen as the iPhone launched on Verizon’s somewhat larger network in February of this year.

It’s possible that rumors of the iPhone coming to Sprint yesterday have merely sparked the rumor mill here. It’s also possible that this source actually does have knowledge of the iPhone coming to T-Mobile. More carriers means more choice for the consumer and will hopefully lead to more aggressively priced plans as they fight it out for a share of iPhone users.

We’ll know for sure in just a few short weeks but until then we’ll keep our eyes peeled for more news on T-Mobile and the iPhone.