How can I encrypt my Apple devices (iPhones, iPads and iPhones)?
Devices (iPhone 4, iPod touch (4th generation), iPad) that ship with IOS 4 have built-in hardware encryption that is enabled if you set the Passcode!
If your device (iPhone 3GS, iPod touch (3rd generation), iPad) originally came with IOS 3 and was later upgraded to IOS 4, then you will need to restore your data in order to encrypt it.