My Wife's G1 works fine in Japan. She used it to call me a few times just a few days ago. Japan (Softbank, who was the only GSM carrier there) recently shut off 2G GSM there so it could ONLY dial out using Band I.
Band I is actually 2100/1900. Most people don't realize 2100 isn't just 2100. It's just called 2100 for short.
As for the 1700 issue it wasn't T-Mobile's call to make. The FCC Made the Decision to make AWS Band IV (1700/2100) when they screwed up and Locked 2G GSM 1900 into the US while the rest of the World was using 1800 for 2G GSM. I hate it when people call Band IV "T-Mobile's 3G". They were the biggest purchaser of the frequency, but Verizon, at&t, Cricket and a couple of other small locals grabbed AWS freqs too. Now that Canada finished their AWS auction a while ago there are 2 providers there that sport AWS.
It was at&t that built their 3G Network to be purely market driven. They had a frequency surplus after Cingular bought AT&T Wireless and decided to use it to "create a 3G network" sharing time with the 2G network and that affected their quality even BEFORE taking on the iPhone. The iPhone just exacerbated the problem. Their 1900 Band II is less compatible with Band I than AWS is, which is why the FCC chose the 2100 Receive Frequencies like they did. So that the AWS and IMT (Band IV and Band I) Freqs. lined up close enough. (I did a lot of research on 3G before the AWS auction.)
I don't really have any love for at&t after my 7 Years with them. I left them just before they got really bad (right before the finalization of the AT&T merger and the name change from Cingular to at&t).
I wish LTE would hurry up to unf*** all this frequency band screw up. LTE bands will be controlled by software as opposed to by Hardware as it is currently. WiMax is a lost cause even Clear knows that since the only support they have in the US is Sprint and has even made comments about changing to LTE. Heck Verizon Just FORMALLY joined the GSMA. So it's the Numbers 1,2 and 4 carriers against the Number 3 carrier for 4G dominance in the US. As for the rest of the world...Every Major Country has chose LTE already. This is why I LAUGH at all those people going gaga over sprint's "4G" network.
Now I'm just rambling. I really hope you didn't think I was trying to be rude or condescending. I just hate when AWS is called "T-Mobile's 3G" while people call at&t's (yes I know Rogers and Telstra use it too) "North American 3G", when it's actually the other way around.
Either way I can't wait to get my Slide.