Yeah I did restore from back up recently.
So it is just showing you the usage from your old phone. If you reset the usage statistics what the phone says will be closer to what AT&T says.
You should be able to look at the bar graph on AT&T's site to determine what your usage has been in previous months. If you never go above 200 MB then you can probably get a cheaper plan. You may want to decide if it is worth constantly checking your data usage and checking WiFi availability before getting a 200 MB plan.
If you are closer to 2 GB some months then you may want to stay unlimited. You may also want to consider what you will use the phone for in the future (video streaming/calling over 3G, or using MyWi) before giving up the unlimited plan.