“Guessing launch day iPhone sales,” writes Oppenheimer’s Yair Reiner in a note to clients issued Friday, ‘has become something of a national sport, a bit like guessing whether Punxsutawney Phil will see his shadow.”

But that doesn’t stop him from playing the game. Reiner’s guess: 1.5 million, one and a half as many iPhones as Apple (AAPL) sold in three days in 2009 and 2008.

Here’s his math:

• 600,000 pre-ordered in the U.S.
• plus 100,000 non- reserved units sold day of at Apple stores (average 500 per store)
• plus 50,000 sold into Best Buy (~45 per store, according to our checks).
• Then multiply by two for international.

We’ll see.

Like Piper Jaffray’s Gene Munster (see here), Reiner surveyed hundreds of buyers Thursday (714 vs. Munster’s 608) and got similar results:

• 76% upgrades, on average after 14.7 months;
• 14% planned to buy an iPad in the next three months;
• 21% were new to AT&T (T), 41% of those coming from T-Mobile (DT) and 28% from Verizon (VZ).

See also:

• 77% of iPhone 4 sales were upgrades
• What’s driving iPhone 4 sales
• What the iPhone means to Apple

[Follow Philip Elmer-DeWitt on Twitter @philiped]