As someone who had a nuclear stress test done a few days before I was scheduled to fly internationally, I asked. I was told it has a half life of 6 hours. While I don't remember the name of what I was given, he did tell me up to 3 days to be completely out of my system.

This isn't true at all, I was in British Columbia for 2 weeks, my cell phone bill went up a few bucks because I did make some calls. The thing that uses data is checking for email which I set to manual and only used while at the hotel on wifi. If the phone is off, it does not do anything, it is off, locked or asleep is a different matter though. I think this idiot set his mail to check every 15 minutes and just went on about his business. The default settings on mail is manual, you need to chenge it to check automatically.