Does iOS 5+ securely erase data on the fly?
No, you need to wipe the entire device using the settings found under Settings > General > Reset > Erase All Contents and Settings. Simply deleting items from iOS applications does not provide any kind of secure deletion, and those files can easily be recovered (although that will be harder and harder as those blocks get overwritten in time).



This provides a one-pass secure delete call that can be liked to OS X's "Secure Empty Trash." While most 3rd party software won't be able to recover your data, government units have far more sophisticated tools that can retrieve data from far worse cases (even physically damaged storage).

This feature was introduced in iOS 2.0 and you can read more about it over at AppleInsider.