ATT told me that as long as I kept Global International data, I was free to switch phone platforms. In fact, I did. I moved from Blackberry to Apple. I was hoping to wait six months and go to Android, but decided that I didn't want to wait and that I could "live with" iPhones from that point forward.
Six months ago, I posted a warning that the trend was to eliminate these plans and urged people to avoid the temptation to be penny wise and pound foolish by switching on the plans only when needed. There are many months I hate the extra $34 I give ATT, but one trip a year pays for it.