I just got back from a three-week trip to China. I'd bought an unlocked Centro on eBay (originally for AT&T) and it worked beautifully with T-Mobile in the US and then in both Beijing and Tianjin with a GPRS SIM card with a one-month data package bought from China-Mobile-Phones.com. The SIM card worked perfectly with no modifications as soon as I arrived in China.

Everything was quite smooth, except that after heavy Chatteremail use I encountered some kind of corrupted database that led to a crashing problem, which I figured out how to fix by deleting the software and reinstalling from the card backup.

There was an occasional network outage with China Mobile, but nothing serious. I had to recharge the voice service once, as I ended up making more calls than expected.

Last year, I had almost the same success with a Treo 650, but there was a problem with sending email by SMTP. This year, I solved that problem by using a special SMTP port. I think that some US internet providers don't readily accept email sent from China, so you have to have some kind of special port setup to avoid that problem, or else set up a Chinese email account and use their SMTP server.

I highly recommend China-Mobile-Phones.com. No affiliation, just a satisfied customer!