In a report to clients issued Monday — five days before the iPad goes on sale — Morgan Stanley’s Katy Huberty says Apple’s (AAPL) Asian suppliers have revised their shipping forecasts for the tablet computer, suggesting strong initial demand. Her key findings:

• iPad suppliers now forecast shipments of 8-10 million iPads in calendar 2010, up from their previous estimate of 5+ million.
• Suppliers now expect to ship 2.5 million in the first three months alone (March to May), considerably ahead of Huberty’s estimate of 750,000 by the end of June.
• Shipments are not sales, however, and Huberty is sticking with her sales estimate of 6+ million iPads in 2010. The Street’s consensus, she says, is closer to 3-4 million.
• Each incremental one million iPads shipped, by her calculation, equates to earnings increases of roughly $0.25 EPS.

According to Huberty, investors who are bearish on the iPad say it lacks a “killer app.” Apple’s near-term market, she counters, is the sub-$800 notebook computer market (30 million units in the U.S. and 120 million units globally). Longer term, she expects the books, magazines, video and iPad-optimized apps currently in the works to broaden that market.

UPDATE: Reports have started to come in from several sources that iPads pre-ordered on March 12 or 13 have shipped to end users, well in advance of the April 3 release date.

[Follow Philip Elmer-DeWitt on Twitter @philiped]