WCDMA v. HDSPA v. UMTS

[inquisitor]

Originally Posted by DRNewcomb

That happens when a carrier has lots of 900 MHz spectrum and not enough 2100. The big problem with UMTS is that it takes 5 MHz per RF channel and a cell needs two channels (10 MHz). While you can build a 2nd rate network with just 10 MHz (one cell "color"), to build a proper system requires 30 MHz (3 "colors"). That's a lot of bandwidth. Many 1900 MHz systems in the US are built on 10 MHz licenses.

You seem not to know a basic difference between GSM and UMTS: While in GSM-networks neighbouring cells must use different channels to avoid interferences and so the "Four color theorem" must be observed, in UMTS all cells use the same frequency. So 2 x 5 MHz (5 MHz for the uplink and 5 MHz for the downlink) is enough for a continious network. Of course you can add additional capacity by running a second UMTS-carrier on separate 2 x 5 MHz-channels.
In Germany all the 4 active operators have just 2 x 10 MHz in the 2100 MHz-band.