I too am visiting Thailand and Southeast Asia this fall and this is what I'm planning to do with my GMAIL account and my 7290 from Cingular...
*Using BIS2.0 services I'm currently synchronized with GMail via Stinsondog's integration guidelines.
*Cingular has unlocked my device, so a foreign SIM chip will work. I'm going to deactivate the voice services w/ Cingular so all calls go directly to voicemail and by doing this I won't incur any int'l voice roaming charges for missed calls.
*Have the Int'l Unlimited data plan so email/data services will work while abroad for no additional cost. The little research I've done, it's difficult to get a prepaid SIM plan with data coverage, so I might just have to switch between my Cingular SIM card and foreign card for voice. Sounds like a pain I know, especially since these java based machines take a long time to reboot but if you can have a real cheap local number, and free data with the Cingular SIM, it might not work out too bad.
So, I'm gonna give this a try for a little while and see if it all works out. Worst off, I can always disable or minimize the Cingular account completely since I'm leaving for 6 months.
Please let us know on this thread if you learn anything to be different or discover a better method.
Best of luck and more importantly safe travels!