How to check the total cellular data used on my iPhone 4S?

My family had recently switched to mobile share plan for AT&T and we now have all iPhone 4S. Our plan is the 10GB one for cellular data and unlimited talk/text. How do I check the total data used for all the lines and also the amount of data used just from my phone?

To Check the amount of data used on your phone:
1) Go to Settings
2) Go to General
3) Go to Usage
4) Scroll down to Cellular Usage
5) Click on It
6) Scroll down to Cellular Network Data
7) Add up the Sent & Received Data to know how much data you've used

1GB= 1024MB