[ducylowycz]

The 3G/3GS iPhone will be able to work on T-mobile's 3G network as long as it's NOT IN THE U.S! T-mobile's U.S. network uses a specific band of 1700mhz for upload and 2100mhz download bands. You have to have both 1700 AND 2100 bands for 3G speeds on T-mobile's U.S. network.

The iPhone Specs. are:
Quad band GSM 850 900 1800 1900 MHz GPRS/EDGE[14]
3G also includes: A-GPS; Tri band UMTS/HSDPA 850, 1900, 2100 MHz[15]
3GS also supports: 7.2 Mbps HSDPA

As you can see the iPhone DOES have the 2100MHZ band HOWEVER does NOT have the 1700MHZ band that is also required. However overseas the standard is quite different.

I know it's stupid and to tell the truth every company in the U.S. should upgrade to standard European 3G bands...it would make everyone's day a little better!!!!