Analysts have interpreted the quick exhaustion of supply as a sign that demand for the iPhone 5 is significantly higher than was the case last year for the iPhone 4S.

"This appears to be well above demand for the iPhone 4S last October," said Brian White, of Topeka Capital Markets, in a note to clients early today after Apple had depleted its pre-order stock. "Clearly, iPhone 5 fever is in full swing."

White has estimated iPhone 5 sales over the first three days -- today, tomorrow and Sunday -- at up to 5.5 million, a number he called "conservative" today in light of his time with the iPhone 5 on Wednesday during Apple's launch. Last year, Apple sold 3 million units in the first three days of the iPhone 4S pre-sales.

"This is a big upgrade," argued White, in contrast to some online criticism that the iPhone 5 doesn't warrant a refresh by consumers. "The thinness and lightness is amazing."

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at , on or subscribe to . His email address is .