Considering updating your iPhone forces you to update to the latest software available for the device, updating an iPhone 3GS now will update it to iOS 6.
iOS 5 will be compatible with iPhone 3GS as well as iPhone 4.
There is no iPhone 3. You may be referring to the iPhone 3G or 3GS, which are the 2nd and 3rd generation iPhones respectively. Out of these two, only the 3GS can run iOS 6, while the 3G is stuck on iOS 4.2.1
No, the iPhone 3GS does not support iCloud. iCloud was introduced with iOS 5, which is not compatible with the iPhone 3GS, as it can only be updated to iOS 6.1.6. Users of the iPhone 3GS can use older synchronization methods, such as iTunes, but not the iCloud service.
To unlock iPhone 3gs on iOS 4.1 you have jailbreak your device first.
Yes. It runs a limited version of iOS 6 excluding several features only because the update would slow the phone down to the point of no usability with all of it.
It uses iOS
Yes indeed! The iPhone 3Gs is still available to buy new, and Apple actually continues making them, infact every iPhone 3Gs bought at this time has already got ios 4.0.1 intsalled on it! but by now ios 4.0.2 is already out, so why keep 4.0.1? ;)
Yes you can, but expect some iOS functionalities that are on, say the iPhone 5S won't carry over to the iPhone 4.
Sadly, no. The latest version of the 3rd iPhone (iPhone 3GS) is iOS 6.1.5.
WhatsApp is not available for the iPhone 3GS, as the app requires a minimum of iOS 10 to function, and the 3GS can only support up to iOS 6.1.6. Moreover, WhatsApp has discontinued support for older devices and operating systems. Users with an iPhone 3GS would need to upgrade to a newer device to access WhatsApp.
Yes. Depend you have an iPod touch 3rd gen +, iPhone 3GS +, or iPad, you can get iMessage and IOS 5.