You cannot. If you buy a new iPod or iPad or iPhone, it comes in iOS 4.3.3 and you have a choice to update to IOS 5 or not.
Yes, when iOS 6 comes out it will be free of charge, just like iOS 5 and iOS 4 were.
Yes you can - when iOS 5 comes out on October 12th 2011.
Probably not. The only OS for iPhone currently in beta is iOS 6. There are is no iOS 5.1.2 currently in beta and iOS 6 should be out within a few weeks. Unless a security hole in the current iPhone OS is found before 6 is released, don't expect an update to iOS 5.
The Apple Message App comes pre-installed on iOS 5.
If you bought it before Oct. 12, 2011, it comes with iOS 4.1, but after Oct. 12th, it comes with iOS 5.0
Yes, Apple iOS 5 is free.
The apple iOS 5 update IS OUT NOW
The apple iOS 5 update IS OUT NOW
Yes you can.
You can update it to iOS 5 the same way you update it to any other iOS version. The 4th generation (and indeed the 3rd generation) iPod Touch can be updated to iOS 5.
iOS 5.1 untethered jailbreak