Data can cost you big bucks if you're not paying attention. This article explains how to check data usage directly from an iPhone or Android phone or through a major carrier, such as AT&T, Verizon ...

Tap Mobile data usage or Wi-Fi data usage, depending on what you want to check. The top of the screen displays your data usage for the current month (as determined by your billing cycle).

This detailed guide covers how to fix the iPhone System Data storage bug with five different solutions without erasing your device.