Following our report yesterday that Apple’s upcoming iPhone 5 will be arriving on the Sprint network, a contact within T-Mobile who claims to have been briefed on the matter has informed us that, in addition to arriving on Sprint at launch, the iPhone 5 will arrive on T-Mobile’s network at launch as well.

The informant, who requested to remain anonymous, went on to claim that the iPhone 5 would also operate at 3G speeds on T-Mobile US network. Current unlocked iPhone 4 units can only operate at 2G “edge” speeds on T-Mobile’s network, and lack certain network-dependent features, such as Visual Voicemail.

Further elaborating on the matter, the informant suggested that T-Mobile USA expects the iPhone 5 to launch sometime in early to mid October, which corresponds nicely with current speculation. He also expects the iPhone 5 to make a significant financial difference to T-Mobile. Our source was quoted as saying the following:

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.

If true, these claims, in conjunction with the notion that the iPhone 5 may launch on Sprint, Verizon, and AT&T simultaneously, could indicate that the iPhone 5 could launch as an unlocked phone capable of use on any network, without containing any carrier restrictions. This would make a high degree of sense, and would serve to ease Apple’s shipping and distribution, as well as making it easier for consumers to choose which carrier they’d like to use.