If your iPhone has an aluminium backing, with a black cover down the bottom then it is a 2G. To differentiate between an iPhone 3G and 3GS, look if you have an app called 'Compass', if you do then you have an iPhone 3GS. The iPhone 4 is easy to identify because it has a flat backing and is more rectangular in shape.
You can download the user's guide for that particular model of iPhone at support.apple.com. You can choose the product manual that you want as well as the language it comes in.
You can sell your old iPhone on amazon.com. Find your model and then list it in the used section. You can also sell it directly to ebay.com or list an auction.
"iPhone" refers to iPhones in general and not a specific model. "iPhone 4" is a specific model. So, they are technically not the same thing. It's more common for people to refer to their iPhone rather than their iPhone 4 though.
The iPhone 3G has Bluetooth and so will the 3Gs model too. I do not know if the 2G model does though.
the latest one called the iphone 4
The white iPhone 3G 16GB
Depends on the model
No, you get the new earbuds with with the iPhone 5. The iPhone 5 is the newest model.
Unfortunatly if you didn't sign up for MobileMe when you bought your iPhone, you are out of luck.
If you want to buy a cheap iPhone case then I want to suggest Gadgetzkart. They provide the best and premium quality iPhone cases at reasonable prices. So, if you want to buy an iPhone case for you any model of iPhone then, It is the best to Place for this.
That is the iPhone 4 GSM. It was the first iPhone 4 released by AT&T.
If you have a newer model iPhone, such as the iPhone 3 or 4, then selling it on eBay should be a breeze. They're one of the most in demand items right now and you should be able to find a buyer without much hassle.