A lot of people don’t have access to unlimited 3G data plans, so they need to keep an eye out on the amount of data they use every month. There are different tasks and apps that will use data on an iPhone or iPad, and it can be hard to keep track of them all. Luckily, Apple has thought of a few ways you can limit access to 3G data by forcing apps to use Wi-Fi instead when it is available.
Take Control Of Your 3G Data Usage [iOS Tips]

