New iPad launch-day estimate: 600,000-700,000 sold

Scattered reports of stockouts and a 9 a.m. headcount of 730 at New York's big glass cube

UPDATE: Apple issued a press release Monday putting first-day iPad sales at over 300,000. They did not offer a number that included Sunday sales.

"It feels great to have the iPad launched into the world -- it's going to be a game changer," said Steve Jobs, in a prepared statement. "iPad users, on average, downloaded more than three apps and close to one book within hours of unpacking their new iPad."

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Even with all the hype that preceded the launch of the iPad -- or perhaps because of it -- Apple (AAPL) managed once again to blow past expectations.

Piper Jaffray's Gene Munster, one of the few mainstream Apple analysts who bothers to count heads, estimates that when the doors opened at the glass cube of New York's Fifth Avenue store Saturday morning, there were 730 customers waiting to get in -- more than showed up for the launch of either the iPhone 3GS (350) or the iPhone 3G (540).

As of 7:30 p.m. Saturday, 19 of the 20 Apple Stores reached by Munster's team still had iPads in stock. But a search of Twitter messages Sunday morning turned up reports of stockouts at many Best Buy (BBY) outlets and several Apple retail locations, including Palo Alto and Santa Clara, Calif., Portland, Ore., and Lancaster, Penn.

In a report to clients issued Saturday night, Munster's estimated that by midnight Sunday, Apple will have sold 600,000 to 700,000 iPads, including pre-orders -- more than double his relatively conservative pre-launch estimate of 200,000 to 300,000. (Other analysts had published estimates of 300,000 to 400,000.)

It took Apple 74 days to sell its first million units of the original iPhone, and three days each to sell a million units of the iPhone 3G and the iPhone 3Gs.

See also:

• Inside the launch day hoopla
• Dawn of the iPad
• Who camps out for an iPad?
• How many iPads will Apple sell?

[Follow Philip Elmer-DeWitt on Twitter @philiped]