Will iOS 6 be available OTA?
It will be available over-the-air, like all releases after iOS 5.0.

That version allowed iOS devices to be independent of any Mac or PC you may sync them to. More information is available from Apple's iOS page:


  iOS updates are free. And they’re available to download wirelessly on your iPhone, iPad, or iPod touch the moment they’re released. Your device even alerts you when it’s time to get the latest version. So you won’t miss out on all the amazing features in new updates.


A device should retain all your apps, content and settings after you update, but it's a good idea to ensure you have a recent backup, either on your computer or iCloud, just in case.