I've got another post here regarding the iPhonetrip simcard for AT&T iPhones. I've used it twice now, and despite significant reservations (Too good to be true? Recommendations from FT users with very few posts?) the darned thing works!

I just got back from China where I used it in my iPhone4s and a jailbroken iPhone3G. Why both? Because the jailbroken 3G becomes a fantastic WiFi hotspot using the $19.99 (one-time fee) MyFi utility. So when I need to use my laptop, I place the sim in the 3G, and when I'm doing light day trips (no laptop) I put it into the 4s.

They have a 1gig (total use) plan for $7.99/day, minimum 1 week, and an "unlimited" plan that runs $11.99/day (and actually has a 7 gig/week cap). I started with the 1gig plan and got nervous it might not be enough so while in China I sent an email and converted it to the higher plan. Didn't need to though, because even with pretty heavy use (constantly using maps, various location apps and more... basically anything you'd like to use an iPhone for while traveling) I still came up with less than a gig over a 9 day span.