The iPhone 4S Fully Utilizes iOS 5
If you opt to upgrade to the iPhone 4S, you'll also have full access to more than 200 new features added to the iOS 5 operating system, as well as the new and revamped apps that come preinstalled with iOS 5, including Reminders and the Notification Center.
Using the iPhone 4S, you'll also be able to utilize iCloud for wireless backup, content streaming, and data and file synchronization, plus take advantage of the improved AirPlay and AirPrint features built into the iOS 5 operating system.
Like the iPhone 4, the iPhone 4S has front- and rear-racing cameras (not offered on the iPhone 3Gs), so you can use the FaceTime app for videoconferencing. Or you can use the revamped Messages app to send and receive free text messages via Apple's iMessage service, or the fee-based text messaging service that's offered by your wireless service provider. If you upgrade your existing iPhone 3Gs or iPhone 4 to iOS 5, you'll be able to experience the vast majority of these new features on the older iPhone models as well.