Watch out iPhone users AT&T is at it again trying to rip you off. Do not sign up for the AT&T Data Plus 200MB monthly data plan because you will likely use this amount of data in the first hour of use if you have a lot of applications running. Also, as you are driving around in the car Apple and AT&T will not tell you that more that half of the data usage is for data signaling as your phone travels between cell phone towers. It has also been reported that the iPhone FaceTime app uses roughly 3MB of data per minute. So even if you are not using your phone to do any of the in the chart below you will still be incurring data charges. Even if you have purchased AT&T's femtocell (Microcell) you will still incur data charges towards your phone usage on the network. This is also appalling and a rip off as well.
We recommend sticking with Wi-Fi as long as you can as the big carriers still think they can take advance of the unsophisticated users. There is still very little transparency and reporting about your data usage and I expect to see many class-action lawsuits as a result. The monthly bills are starting to come in and if you are not diligent you may find yourself in cell phone billing hell. These figures above pertain to other smartphones and do not represent normal data usage on iPhones.