Apple Inc said on Monday it sold 4 million iPhone 4S in the new smartphone's first three days on the market, setting up a strong December quarter for the world's largest technology company.

Helped by availability in more countries and on more telecommunications carrier networks, the iPhone 4S, which went on sale on Friday, October 14, managed to outshine the iPhone 4, which sold 1.7 million over its first three days.

Unveiled just a day before Apple Chairman Steve Jobs died, it was initially dubbed a disappointment, partly because it looked identical to its predecessor. But anticipation of its Siri voice software helped it set an online record in pre-orders on October 7.

It hit seven countries -- Japan, Australia, France, the UK, Germany, Canada and the United States -- versus five for the iPhone 4. In the United States, it launched with all three major U.S. carriers -- Verizon Communications Inc's and Vodafone Group Plc's Verizon Wireless, AT&T Inc, and Sprint Nextel Corp -- rather than just one for Apple's previous smartphone. In Japan, it appeared on KDDI Corp's network for the first time.

Availability in more countries and carriers is helping unit volumes, in addition to pent-up demand, said BMO Capital Markets analyst Keith Bachman, adding that the mix of phone models sold will help margins during the last quarter of the year.

Wall Street analysts expect Apple to chalk up 25 million to 30 million iPhone sales in the final three months of the year, despite worries about a tepid consumer-holiday season.

The company took more than 1 million online orders in the first 24 hours when iPhone 4S was available for pre-ordering, exceeding the 600,000 pre-orders received for the iPhone 4 when it launched.

On Monday, Apple also said that more than 25 million customers were using the iOS 5 mobile operating system in the first five days of its release. And more than 20 million customers have signed up for iCloud, its free cloud services, Apple said.

The latest iPhone will be available in 22 more countries on October 28 and more than 70 countries by the end of the year.

Shares in Apple were down 0.9 percent in afternoon trading to $418.18, alongside a decline in the broader market, after staying in positive territory for much of the morning.

(Reporting by Supantha Mukherjee in New York and Poornima Gupta in San Francisco, editing by Gerald E. McCormick)