By Neil Hughes

Published: 08:10 AM EST (05:10 AM PST)

With Apple selling out of its first run of iPad preorders, one analyst has upped his estimate for debut, first-quarter, and 2010 iPad sales, predicting the company will likely sell more than 2.7 million this year.

Gene Munster with Piper Jaffray said Thursday his initial estimates of 900,000 sales in the June quarter and 2.7 million in calendar year 2010 "may prove to be conservative." He has compared the introduction of the iPad to the iPhone debut, when Apple sold handsets for $499 without contract in 2007. The original iPhone sold 270,000 at launch.

"We believe early indications suggest that initial demand is stronger than the company expected and/or supply issues have slightly constrained availability for the launch," Munster wrote.

The analyst noted that Apple said on Saturday that new iPad orders won't ship until April 12, and on March 31 the company's retail stores began calling those who reserved and iPad for pickup to confirm their purchase.

"We believe these signs indicate that initial demand for iPads was stronger than the company expected, and/or minor supply issues have slightly constrained availability for the launch," Munster said. "We believe the supply constraints are minor because the new ship date is not a significant delay. Ultimately, both strong demand and somewhat constrained supply appear to be resulting in the fact that Apple is selling every iPad it can build."

Last week it was reported that Apple switched its touch-panel orders to Wintek, as its previous supplier had experienced delayed shipments. When the company began accepting preorders, it limited the number of purchases to two per person. Apple also turned down volume orders for businesses. These actions fueled speculation of a tight iPad supply for the product's launch.

Weeks ago, a handful of reports of manufacturing constraints suggested initial supply of the iPad could be limited, with a launch limited to 300,000 units. But another repor alleged that suppliers have had no issues in the manufacturing of the iPad, and expect Apple to ship between 600,000 and 700,000 devices at launch. That report claimed Apple would have the capacity to ship another 1 million iPads by the end of April.

Also Thursday, analyst Brian Marshall with Broadpoint AmTech issued a note to investors in which he focused on the content that will be available for the iPad at launch. He noted that the iBookstore from the App Store will offer "most" titles from major publishers, including Hatchette, HarperCollins, Simon & Schuster, Penguin, Macmillan, Perseus and Workman, as well as magazines from Conde Nast, Time and Hearst.

Earlier this month, Marshall predicted that content sales will equal nearly 30 percent of the revenue Apple will earn from selling the hardware by the end of 2011. He said the "sticky" nature of the iPad and content purchases for the new device will see content revenue top 10 percent of hardware revenue by December of 2010.