Apple's latest device iPhone 4S preorders were sold out at wireless carriers AT&T, Verizon and Sprint on Thursday, Oct. 13, just one day before the device officially hits the retail shelves.
 
Even without design changes, iPhone 4S is still a potential bestseller featuring iOS 5, iCloud, A5 dual-core processor, an 8-MP powerful camera and a cool voice assistant tool Siri. Its design, however, remains unchanged - 3.5-inch retina display, glass back and two cameras.
The iOS 5, released on Oct. 12, has more than 200 new features that could make iPhone 4S a bestseller. These new features include iMessage, reminder, Notification Center, Game Center, and Safari. The iOS 5 is available on the iPhone 3GS, iPhone 4, iPhone 4S, iPad, iPad 2, and iPod Touch third- and fourth-generation. 
 
Although the upgrading error message of iOS 5, error3200, resulting from the extreme demand as iOS 5 was released, has bothered many users, people have found many ways to fix it, such as just waiting, or repeating the update attempt.
 
With iOS 5 and Siri, iPhone 4S will undoubtedly become the bestseller in the smartphone war. Following are some reasons why:
 
Siri
Siri, a voice-recognition and voice-synthesis system, runs only on iPhone 4S. Siri allows you to use your voice to do many things, such as sending message, scheduling meetings, placing phone calls. Remind me to call the vet. Any good burger joints around here? Siri does what you ask for. You can work and play at ease with this powerful assistant.

iCloud
iCloud can store music, photos, documents, and more and wirelessly pushes them to all user's devices. iCloud automatically and securely stores the content so it's always available to user's iPhone, iPad, iPod touch, Mac, or PC. Apple said its way is automatic and effortless. When people sign up for iCloud, they automatically get 5GB of free storage. It gives users access to your music, apps, latest photos, and more from whichever device users happen to be using.
 
iMessage
iMessage is an instant messenger application developed by Apple for iOS 5. iMessage allows users to send texts, photos, videos, contact information and group messages over Wi-Fi or 3G to other iOS 5 users. People can also send a message to one person or to many friends at once - along with photos, videos, or links they like. When someone replies, everyone can see it.
 
Tweet Everything
After signing in once in Settings, you can tweet directly from Safari, Photos, Camera, YouTube, or Maps, via iPhone, iPad, or iPod touch. People can also add a location to any tweet. 
 
Notification Center
Notification Center can make sure you know all your imminent event, such as email, texts, calendar events, friend requests, game notifications, breaking news, latest scores.  Notification Center keeps track of all the recent alerts in one convenient place. You can get a quick summary of individual actions from the lock screen.

Newsstand 
With using Newsstand, iOS 5 help you organize your magazine and newspaper app subscriptions. As new issues become available, Newsstand automatically updates them in the background with the latest covers. New purchases will go directly to your Newsstand folder.