I had this same problem. It only happens on two phones on our plan, both iPhone 5ses. One from Dec 2013, one from Nov 2014. After looking in to it and reading over several posts in different forums, I am pretty sure it is just the amount of data that is used every 6 hours all added together. For iPhones, if you go to Settings, Cellular and then scroll to the very bottom, you can reset your statistics. Then monitor how much data you use for 1 day and what apps are using it. The apps that were using a lot of data for us were: Mail, Safari, Maps, Facebook, Instagram, Twitter, and Snapchat. Every time you load these while you are not on WiFi, it uses a lot of data to download whatever information you want. If you are bored and downloading a lot of pictures or videos (thanks Facebook for autoplaying them all for us and using our data like crazy...) without even realizing it, you could rack up the data pretty fast. Add all of that up in a 6 hour period and it could seem like a very large chunk, especially when it updates the data information while you are asleep. If you want to prevent yourself from using your cellular data for these applications, you should be able to turn them off on that same Settings, Cellular tab. I haven't done this for most of my apps personally because I only need to use Maps while I am driving around without WiFi, but it would help to remind me that I can wait until I get somewhere with WiFi to check out all of my friends on social media. As for the other iPhones on our plan, a 4S and a 6, they don't update the data every 6 hours. The 4S is kind of random so I'm not sure how often that is updated, but I think the 6 is every time you use data. We have pages and pages of data log for the iPhone 6. Anyway, I hope this helps all of you that are going over your data every month. It's not a fraud, but I am disappointed that no one from Verizon has figured this out earlier for all of us iPhone 5s users.