Early sales figures dwarf analyst estimates.
Analysts have reported that Apple sold more than 500,000 iPhones in the first two days after launch.
A report by Piper Jaffray claimed that over half a million iPhones were sold through Apple and AT&T stores. The financial research firm had originally estimated that just 200,000 units would be moved in the first two days.
"Apple met strong demand over the weekend with adequate supply," wrote Piper Jaffray analysts Gene Munster and Michael Olson.
"We were surprised by the rate at which Apple was able to sell the handsets, with 50 cashiers processing up to 1,000 iPhones per hour in some stores."
Other analysts offered similar reports. The Los Angeles Times cited analyst Trip Chowdhry of Global Equities Research in estimating that roughly 525,000 iPhones had been sold. Chowdhry could not be reached for comment.
Piper Jaffray also conducted a preliminary survey to find out who was purchasing the iPhone. A survey of 253 users found that three-quarters were Mac users, while more than half were new customers to AT&T, the sole operator for the iPhone.
The US$599 8GB model was overwhelmingly preferred, accounting for 95 per cent of purchases.
The analysts said that the brand loyalty of iPod and Mac users could be a decisive advantage for Apple over other mobile device vendors.
Former Apple partner Motorola is bearing the brunt of that loyalty, according to the survey, as 35 per cent of respondents upgraded to the iPhone from a Motorola device.
Nokia and Treo were next on list, with 13 per cent of respondents. Only six per cent of those surveyed said that they would be giving up a BlackBerry in favour of the iPhone.
The survey suggested that Apple's pitching the iPhone as a convergence device may not be a big selling point. Some 68 per cent of respondents said that they still plan to use an iPod in addition to the iPhone.
Apple did not return a request for comment on the reports. The company has declined to comment publicly on the number of iPhones it has sold or how many it had in stock prior to Friday's launch.