So I'm on AT&T with an iPhone 3GS right now, and I'm lucky enough to be grandfathered into their unlimited data plan. However, T-Mobile's free global data is really appealing to me for the 3 or 4 weeks out of the year I travel, and for keeping in touch with international friends. I know T-Mobile claims to offer unlimited data, although in the past this was capped at certain amounts. Do these caps still exist? I spend most of my time in New York City, where I'd imagine T-Mobile's network would have to be pretty good at this point. Bottom line: is the global data a good enough reason to jump to T-Mobile for me when I upgrade my iPhone? Or should I stick with my grandfathered unlimited plan through AT&T?