I will be going to the US on Wednesday with my wife and 2 girls. They all have Canadian plans with 1GB of data. The girls will get the US talk and text plans but no data. My wife will get a US talk, text, and data. I know I could just turn their data off but it sometimes "magically" turns itself on. Will the data block prevent the girls from using data (not wifi) in the U.S? Also, once my wife gets close to her 750MB of U.S. data (shock free would be great here), can I put on the data block so that she won't "accidentally" turn on her data? Thanks!