Brendan Mcdermid/ReutersCustomers stood in line to buy the iPhone 4S in New York on Friday.

People were O.K., it turns out, with an evolutionary iPhone.

On Monday morning, Apple said it sold more than four million iPhone 4S’s during the device’s first few days on sale after its Friday release. That figure is more than double the 1.7 million units of the iPhone 4 that Apple sold during its first three days on the market in June of last year.

The results seemed to be a vindication of Apple’s decision to offer what amounted to an upgrade of the iPhone 4 with its new model, rather than a wholesale makeover. The new phone’s look is virtually identical to the exterior design of its predecessor, though it has better internal hardware and a new virtual assistant feature, Siri, which uses voice recognition to handle various tasks. Initially, there was some disappointment that Apple didn’t release an iPhone 5 with bolder cosmetic changes on the outside of the device.

An analyst with RBC, Mike Abramsky, called the iPhone sales “monster” in a research note on Monday morning, noting that he had expected Apple to sell three million of the devices sold during its first weekend. Mr. Abramsky noted that sales could have gotten a lift from broader distribution of the phone at its introduction, including Sprint and Verizon in the United States.

Apple released some other impressive numbers Monday morning, saying that 25 million of its customers have already begun using iOS5, the new version of its operating system for iPhones, iPads and iPod Touches. Apple also said 20 million customers have signed up for iCloud, the free service that lets people synchronize and save data on their Apple devices.

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