My 2 cents of thought: Whenever you are using the 8830 abroad (Outside US), you NEED to call CSR at least 3 working days to temporary switch the BIS/BES unlimited worldwide plan in order to take advantage of the unlimited data service. I had learned the hard way. I'd call the night before I depart for Asia, trusting the CSR to switch me to Int'l data service (Without asking them for any confirmation # or email). To my dismay when I received my following bill I'd almost fell off my freakin chair! Lesson to be learn!
As far as the roaming capability, it roams both CDMA & GSM in Asia. The data part, I'll suggest you switch to "GSM" mode as it seem to be faster for emails and thethering. I'd tried plugging in local prepaid SIM card for regular voice calls, it works fine (Unlike Verizon, which is locked).
I hope this will shed some lights to this wonderful device.