Barclays Capital said Apple Inc.'s iPad 2, which began shipping in the U.S. on March 11, remains sold out across retailers with limited sporadic availability at Apple stores themselves and 4-5 week wait times via Apple.com.

As a reminder, the iPad 2 is expected to be available in 25 additional countries later this week -- but we wouldn’t be surprised if some international launches were pushed back and/or met with limited quantities available given the lack of availability in the U.S. (the Japan iPad 2 launch has already been delayed), said Ben Reitzes, an analyst at Barclays Capital.

While there are some overarching concerns regarding the tablet/PC and smartphone supply chains following the devastation in Japan, Reitzes does not believe there is any impact on calendar first quarter shipments for Apple.

With iPad 2 shipments solidly beginning in March, Reitzes believes his estimates calling for unit sales of 5.1 million look quite conservative for Apple's March quarter -- in the many hundreds of thousands.

Reitzes estimates 28.83 million iPad units for fiscal 2011 (33.7 million for calendar 2011) and 40.02 million for fiscal 2012 (42.1 million for calendar 2012), which are likely quite conservative as well although significant upside to his estimates for calendar 2011 could depend on potential supply constraints.

That said, we believe some recent concerns may be overblown. In our recent checks, builds for non-Apple tablets were on the downswing while Apple demand was very strong, said Reitzes.

Reitzes said most major Apple products are shipping within 24 hours on Apple.com with the exception of the 12 core Mac Pro and the Mac Pro Server, which are shipping within 2-4 business days, and new iPad 2 stock keeping units, which continue to show shipment time delays of 4-5 weeks.

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Reitzes said Apple’s new iPad 2 stock keeping units are also listed on BestBuy.com and Walmart.com but neither retailer is showing any readings on iPad 2 units available in stock at respective retail stores.

Motorola Xoom moves to number one in top tablets at Amazon.com at $599 but only since iPad 2 is not available. Reitzes said tablet average selling price at Amazon.com is $537 this week versus $599 last week. Reitzes continues to believe the tablet average selling price will continue to go down as new launches from Apple's competitors is expected by mid year.

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