How to monitor your mobile data use easily on iPhone
You might want to continuously monitor your data usage
Instead, what you might want to do is to set up a widget in your today panel that you can quickly access and customize to show you just how much data you've consumed in a given period.There's a plethora of such widgets on the Apple App Store, but we'll show you just one that works great for us: Traffic Monitor. It's a dedicated free app that comes with a widget that shows you both the data you use on Wi-Fi and cellular, and allows you to know how to better organize your data usage. We walk you through the installation and show you how it all looks right below.
Things that are NOT allowed: