Without getting too off topic, Wikipedia seems to indicate otherwise (
http://en.wikipedia.org/wiki/UMTS_fr...bands#UMTS-FDD). This shows a UMTS 2100 uplink of 1920 - 1980 MHz, and a PCS downlink of 1930 - 1990 MHz. So AT&T, for example, could use the standard 2100 MHz band. Right?
Also, you mention that T-mobile doesn't have access to the 1900 MHz band. T-mobile ONLY has 1900 MHZ (PCS) coverage.
Originally Posted by
typical
The problem isn't the 2100 MHz spectrum at all. It's the 1900 MHz.
The original UMTS standard was 1885–2025 MHz uplink and 2110–2200 MHz downlink. This is known as "2100 MHz" or sometimes "1900/2100 MHz". It's what most of the world uses.
However the 1900 MHz band was already being used for 2G services in the US. Hence AT&T could replace some of its 2G spectrum for 3G, using 1850-1910 MHz for uplink and 1930-1990 MHz for downlink. This is why AT&T's 3G is incompatible with most of the rest of the world.
T-Mobile, without access to the 1900 MHz band, could still use 2110-2155 MHz for downlink but was forced to use 1710-1755 MHz for uplink. Hence the incompatibility with everyone.