It allows you to roam and use data on another network. As long as you have unlimited roaming you won't be charged, but sprint can terminate your contract if you use to much, so I wouldn't advise doing any over excessive streaming I think they cap that so called unilmited roaming off at about 5GB. All I know is since I turned it on my mobile connection hasn't disconnected one time and I'm now able to use data in places I was not able to use prior. I just make sure I uncheck it when not needed.