We have learned iOS 6 new features, and they are amazing, however, seems not all iDevice can get all the brand new iOS 6 new features. Here's Apple's list of limitations that reveals which devices get which new iOS 6 features. Notably, the iPhone 4 does not get FaceTime over 3G, Flyover, Turn-By-Turn Navigation, or Siri.
● Flyover and turn-by-turn navigation will be available only on iPhone 4S and iPad 2 or later. Cellular data charges may apply.
● Siri will be available only on iPhone 4S and iPad (3rd generation) and requires Internet access. Siri may not be available in all languages or all areas, and features may vary by area. Cellular data charges may apply.
● Shared Photo Streams requires iOS 6 on iPhone 4 or later or iPad 2 or later, or a Mac computer with OS X Mountain Lion. An up-to-date browser is required for accessing shared photo streams on the web.
● FaceTime over a cellular network requires iPhone 4S or iPad (3rd generation) with cellular data capability. Carrier data charges may apply. FaceTime is not available in all countries.
● VIP list and VIP and Flagged smart mailboxes will be available on iPhone 4 or later and iPad 2 or later.
● Offline Reading List will be available on iPhone 4 or later and iPad 2 or later.
Made for iPhone hearing aids require iPhone 4S.
You can read this to learn more about iOS 6.