With a multi-nation international roll-out, Apple's iPhone 4S, the last iPhone to be unveiled in the company's iconic co-founder Steve Jobs' lifetime, will be up for pre-order from Friday midnight. The flagship smartphone from the Cupertino-based tech giant will be available from Apple.com and run on AT&T, Verizon and Sprint.

The iPhone 4S was launched with a thud on Thursday, outraging fans who had expected for a revolutionary new iPhone 5 after a long wait of more than one year. Yes, the iPhone 4S was just not the brightest moment for Apple, but it does have enough advantages to justify an upgrade from your older iPhone.

According to Wall Street analysts, with software enhancements and a sprinkling of new features, iPhone 4S would keep Apple's leadership in the growing smartphone competition intact. Here is our take on five significant reasons why upgrading to the iPhone 4S makes sense.

Siri: A natural voice recognition - this is the feature that will attract most of the users. Siri is a built-in digital assistant, which takes voice commands and translates speech into text in English, French and German, though more languages will be added later. Siri allows iPhone 4S users to tap their home button and simply prompt the phone to assist, including time inquiry, making a call, searching the web and finding restaurants.

Carrier Diversity: Sprint has accompanied Verizon Wireless and AT&T as the third wireless carrier to support the iPhone. While AT&T can provide 4G-like data speed, Verizon has the most reliable voice network. When it comes to Sprint, it is the only carrier to offer an unlimited data plan, and if you are thinking about an unlimited data plan, you should go for the Sprint iPhone 4S.

Sprint, which has waited for years to get the opportunity, is likely to boost iPhone 4S sales, especially among customers in the Midwest and among lower-income users, according to analysts.

Upgraded Camera: The iPhone 4S camera has an 8-megapixel sensor that takes 3264 by 2448 pixel pictures. It will capture more vibrant photos, especially in low light. The camera is claimed to be 30 per cent sharper. It comes with an aperture of f/2.4. The video camera will be able to capture video in 1080p HD.

According to Apple, the new iPhone 4S can take the first picture after 1.1 seconds and the second one after half a second. The company also promises a lens that delivers backside illumination which provides increased light to the sensor.

More Power, More Speed: The iPhone 4S comes with a dual-core A5 processor, which is expected to deliver two times faster CPU performance and up to seven times faster graphics performance. With HSDPA (High Speed Download Packet Access) technology, the device is claimed to have faster data download speed, nearly twice as fast as the iPhone 4 - 14.4Mbps compared to 7.2Mbps.

Getting faster doesn't mean that users will have to pay the price with battery life. The iPhone 4S battery will provide eight hours of talk time, six hours of Internet surfing and nine hours in Wi-Fi mode. Users can watch movies for 10 hours and play music for 40 hours.

The World Phone: With both CDMA and GSM networks, the new iPhone 4S functions as a world phone. During the Let's Talk iPhone event, Apple CEO Tim Cook mentioned that 93 per cent of Fortune 500 companies are testing and deploying iPhones in their workplaces. Thanks to the CDMA and GSM network supports, the iPhone 4S can roam on GSM networks in 200 countries, which makes it quite appropriate for business purposes. According to analysts, for a lot of users who travel internationally, the world phone is a big thing.

In addition to these five key features, the iPhone 4S incorporates a unique technology for better reception. After the launch of iPhone 4 last year, users found that holding the device a certain way led to dropped calls. With the new iPhone 4S, Apple seems to have fixed the glitch. It features a unique technology that switches a radio signal between its two antennas to send and receive - a new feature that is expected to provide better reception.

Although Apple's shares fell heavily after the announcement of iPhone 4S, analysts believe that the new device's sales won't get hurt. They pointed out that although the transition from the iPhone 3G to the 3GS was similarly incremental, that didn't stop buyers from buying it up in record numbers, Reuters reported.

According to Ticonderoga analyst, Brian White, Apple is expected sell 27 million iPhones in the October-December quarter. The iPhone 4S costs $199 for the 16GB model, $299 for the 32GB model and $399 for the 64GB model.