Apple’s iPad tablet device is shipping April 3 and already it’s looking like another hit for Steve Jobs & Co.

Morgan Stanley analyst Katy Huberty in a recent research note expects 8-10 million iPad shipments this year with sales of 6 million. More than 2 million of those sales should occur in the first three months, she added. That’s an upgrade from her previous shipment estimation of 5 million for the year, and more bullish than the current sales consensus expecting 3-4 million devices sold.

Apple over the weekend announced that pre-orders guaranteed for delivery on April 3 sold out. Any pre-orders taken after this weekend likely won’t be delivered until April 12. Somewhat tempering sales is that only the WiFi version of the iPad will be available initially. iPads with a combination of WiFi and 3G cellular connectivity won’t be available until late April, and many potential buyers may be waiting for the broader functionality before buying.

In addition to being available in all Apple retail locations, the company says most Best Buy stores will also carry the device starting April 3 as well.

Still up in the air, however, is the application environment. Few details have been shared about what kind of content iPad owners will have access to once the device is finally available. A recent comScore survey suggest that music applications rank third in terms of interest among potential buyers, trailing Web surfing and e-mail. However no iPad-specific music applications have been announced. Instead, most of the iPad related content news trickling out in the weeks before availability has focused on magazine and newspaper subscriptions, as well as books.