The pre-orders for iPhone 4S have started and it might be hard to tell the difference between it and the iPhone 4 as far as the exterior of the smartphone is concerned. But what is important is what lies under the hood and, in this regard, iPhone 4S boasts of some amazing features that have made it the most-wanted device at the moment.

The iPhone 4's price was dropped to $100 for an 8GB model. The iPhone 4S will cost $200 for the 16GB model, $300 for the 32GB model and $400 for the 64GB model. But all require a two-year contract for those special rates. The iPhone 4S is quite a bit more powerful and faster than the iPhone 4. But each smartphone will be getting an iOS 5 upgrade when the iPhone 4S is released on Oct. 14.

Here are the upgrades being released on the iPhone 4S so you can decide if the features are worth the extra $100. Click the slideshow to begin.