Apple is set to sell over 4 million units of its new iPhone 4S this weekend after customers around the world queued to buy one of the last products developed under Steve Jobs.

Hundreds of fans queued around city blocks around the globe Friday to be the first to get their hands on iPhone 4S.

iPhone 4S has significant hardware upgrades, though it looks identical to the iPhone 4. It is equipped with an A5 chip, iOS 5, Siri Voice assistant and an 8-megapixel camera along with many features. It is available with a new 2-year contract for $199, $299 and $399 for the 16GB, 32GB and 64GB models of the phone respectively. The phone is available on AT&T, Sprint and Verizon Wireless.

Apple received more than 1 million pre-orders in the first 24 hours after iPhone 4S had gone on sale. This has toppled the previous record of 600,000 set by iPhone 4 last year. Demand was so high that the Apple Web site said new orders wouldn't ship for a couple of weeks.

If Apple sells 25 million iPhones, it will be up by 77 percent from the 14.1 million handsets Apple sold in the September quarter of 2010 when the iPhone 4 debuted.

Apple CEO Tim Cook and his executive team hope that iPhone 4, launched without the firm's former visionary leader at the helm, will safeguard Apple's global market share against a growing challenge from the likes of Samsung.

It appears that iPhone 4S has taken over the champion attributes from its precursors and is ready to carry on and fortify Apple's position in the smartphone market. This was much needed for Apple to face the stiff competition from Samsung with smartphones powered by Google's Android software.