Because the chip in the 3G iPhone doesn't support the 3G T-Mobile provides, the current iPhone cannot be used on the T-Mobile 3G network. http://www.breakitdownblog.com/3g-iphone-may-not-work-on-t-mobile-3g-network/ This is because the 3G networks have different frequencies. If you look at the tech specs for the 3G iPhone, you can see it doesn't support T-Mobile's 3G network.http://www.apple.com/iphone/specs.html As you can see from that, the iPhone only supports UMTS/HSDPA (850, 1900, 2100 MHz) GSM/EDGE (850, 900, 1800, 1900 MHz) However, T-Mobile's 3g Network uses 2100 and 1700. http://www.technewsworld.com/story/62876.html Thus, the iPhone 3G cannot get 3G signals from the T-Mobile 3G network. However, that is what we have already known. Now, the question is, will the third generation iPhone support T-Mobile's network? It seems to me and many others that Apple will be using this chip: http://www.electronista.com/articles/08/05/31/infineon.xmm.6180.3g.chip/ The X-Gold 618 PMB 9800. However, the question is, will this chip support T-Mobile's 3G network? If anybody knows anything about this topic, it will be appreciated. Thanks!