For both myself on the Samsung Galaxy S4 and my girlfriend on an iPhone 5c, both of which we got just a week ago, we see our data usage total increasing several times a day, typically in very small amounts, occasionally larger. Her increases are about 10x larger than mine overall. All of this happens when we're each on wi-fi so I wouldn't expect to see these increases then. Any idea why this is happening and what I can do to prevent it? I'm guessing it may be some sort of auto update processing happening in the background, but I don't know that for sure and don't know what else could be causing this.