If you want international 3G, go with T-Mobile. By practice, all T-Mobile smartphones ranging from their current Android smartphones even to their previous generations of Windows Mobile, have an optional 2100 3G band for Europe and Asia roaming. Of course, understanding that T-Mobile USA is owned by T-Mobile Europe aka Deutsch Telecom is a factor in this.
If you happen to unlock any T-Mobile smartphone, it will work with any SIM from any Asian or European carrier. (Note: Japan with Softbank, China with Unicom, Australia with Vodafone and Optus).
My first Android was a MyTouch 3G, unlocked, which I managed to work with Asian 3G frequencies.
So yes, the G2, MyTouch 4G, Nexus S, Nexus One, will all work.
If you're traveling overseas, I suggest if your T-Mobile smartphone isn't unlocked yet, to use a Nexus One or Nexus S and purchase one of the prepaid data SIMs. Note that some of these SIMs will give you unlimited data access only for a few days, but without voice and text, turning the phone into a mobile internet device only. In many cases, the voice and text only prepaid SIM is separate, which you can use in any unlocked cheap GSM phone (like cheap Nokias).
Some other US Android phones do have international 3G frequencies.
Samsung Captivate
Droid 2 Global
HTC Merge (soon to come to Verizon)
Requires to be unlocked.
Overseas, you can find unlocked Androids, but you must still be willing to pay a few hundred dollars for them. The last time I saw a sale in the Phillippines for around $150 for the LG Optimus P500 (Optimus One). Normally though, this phone would cost nearly $300 no contract, unlocked, no subsidy. I would recommend this because its higher spec'ed than the Huawei Ideos, Vodafone 845, LG GT540, Samsung Galaxy 3, Galaxy 5, HTC Tattoo or HTC Wildfire. The Orange San Francisco (ZTE phone) seems decent though.
The Huawei Ideos, itself not bad as a budget Android phone, should be seen as a mobile wifi hotspot with a phone function attached to it. Not surprising since Huawei is the dominant supplier of 3G dongles and MIFI sets around along with ZTE.