iPhone - FaceTime - Can I use FaceTime over cellular data?

Some wireless providers are limiting FaceTime over cellular calling to subscribers with specific data plans. Although iOS 6 provides for FaceTime over cellular, how can you tell if your iPhone has this capability?

To determine whether or not you have access to FaceTime over cellular, or you are limited to only making video calls over Wi-Fi:

On your iOS device navigate to Settings -> FaceTime -> Use Cellular Data -> ON

On newer versions of iOS the toggle is located here: Settings -> Cellular -> FaceTime -> ON

If nothing happens, you should be ready to make and receive FaceTime calls over your cellular data connection.

If your data plan is not eligible you will be limited to FaceTime over Wi-Fi and a pop-up box will appear with the following message:

FaceTime over Cellular

"FaceTime requires an active Wi-Fi connection or an eligible cellular data plan. To enable FaceTime over cellular on this account contact [wireless provider name here]."