That's a shame that you were not aware of this issue. It's actually been the case all along, but many consumers do not understand it. 3G is a generic term meaning high speed data that operates on WCDMA bands. (Even GSM phones use WCDMA for their 3G data networks) It is not a Cingular specific term. They just chose the 3G moniker for marketing purposes.
The 2100 band in the US is used by the military, and as such will never be available for any carrier to use in the USA. (unless the military switches bands and releases the 2100 band for public use)
So US carriers were forced to use whatever bands the FCC made available. For GSM, that meant the existing 850 and 1900 bands. TMobile USA recently purchased a newly opened 1700 band for their upcoming US 3G network as well. Meaning that people that want to use their new network will not be able to use ANY existing phone. New phones with a 1700 band radio will need to be produced.
Now most phone manufacturers are releasing phones with both the international band (2100) and the US bands (850/1900) for their 3G networks, and I'm sure some will even add the new TMobile 1700 band once they get it up and running. However, all these 3G bands actually use WCDMA for these bands, not the GSM bands used for voice calls.
CDMA and WCDMA are tecgnologies largely patented by Qualcomm. However, Nokia is in a legal dispute with them over the use of CDMA technologies and licensing royalties. As a result, you rarely if ever see a Nokia phone on Verizon or Sprint since they use CDMA phones. Cingular and TMobile use GSM phones like the rest of the world, so you can get Nokia and Sony phones for their networks.
However, As I mentioned before, even GSM phones use WCDMA for their hi speed data networks. So to minimize the amount of royalties Nokia has to pay Qualcomm during the legal battle, they are only licensing the technology for the 2100 band, since it is the one used everywhere else in the world.
The reason Sony Ericsson is also involved is that both Nokia and Sony Ericcson use Symbian smartphones exclusively. A large part of Symbian is owned by Nokia. So since Nokia is unwilling to incorporate US CDMA bands until the legal dispute with Qualcomm is settled, and Nokia controls Symbian, the Sony Ericcsson phones fall into the same problem.
Therefore it is unlikely you will ever see a Nokia or Sony phone support hi speed data in the US until the case has been settled. Even the brand new flagship Nokia N95 and E90 phones (which might even be sold in the US) will have this issue. They will work on the hi speed 2100 band all over the world, but in the US it will max out at EDGE speeds. EDGE uses GSM, so there is no issue with Qualcomm.
If the legal dispute is settled, then you will probably start seeing Symbian based 3G phones in the USA very quickly. It's a large market they are being shut out of, so a settlement will bring them back in a hurry.
But if it is never settled, then there are only two answers. One, the 2100 band becomes available in the US and Cingular and TMobile make it available. Or two, a new non-CDMA based technology emerges for hi speed data that Qualcomm does not control. One possibility is Wi-Max.
Sprint is planning on using Wi-Max for their future 4G data network, and many others are also looking into it. However, since Sprint uses CDMA for voice calls (like Verizon) they still will not be able to get many Nokia or Sony phones. But if Cngular or TMobile USA decide to adopt Wi-Max, then that would open the door for Symbian based phones to finally offer hi speed data in the USA.
China is also working on their own 4G protocol that they are trying to get the international community to adopt. As long as there are not huge licensing fees like Qualcomm charges, Nokia would likely jump on board, and as a result Sony with them.
The last option would be if Sony turned their back on Nokia and started including the bands on their own. But that may jeopardize their licensing agreement with Symbian. They could always switch some of their phones over to Windows Mobile or Linux platforms, but I don't think they want to abandon Symbian since it is still the most prevelant platform used in the world today. So that option is unlikely. As Nokia goes, so does Sony... for now at least.
Hope this helps other when making a choice of phone and carrier in the future.