no
Not without jail breaking it.
iPhone 3gs are more roundish and without Siri. The edges instead of being straight are round. The iPhone 4g has square edges without Siri. The iPhone 4s is just like the 4g instead it has Siri. The iPhone 5 is longer and has Siri. The iPhone (original) has round corners and is small. Same with the iPhone 2. If you have a iPhone or iPhone 2 you can replace them. Also, the iPhone 3gs is not out so you cannot buy it anymore. Only the 4, 4s and 5 are out. They will be getting rid of the iPhone 4 soon.
I would say it stands for Siri. More specifically "Siri Voice Recognition", since the regular iPhone 4 does not have Siri (by default). But I can't find any official documentation to back up this answer.
yes
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.
Use a hammer
yes
iPhone 3gs
iPhone 3GS
Only with an app on iPhone 2G 3G 3GS or 4. On 4S you can use Siri
Dose the iphone 3gs have a radio