“In January,” he wrote, “Apple reported a monstrous 37 million units for the December quarter, followed by an almost equally strong March quarter of 35 million units… Our view is that iPhone unit estimates may end up being too high near term, and with the stock at $611 it presents some risk.”

Blair is looking for Q3 sales to come in between 28 and 30 million units.

“We would be cautious,” he concludes, “if consensus expectations for units shape up to be 31 million units or higher for June.”

That’s interesting, because in our survey of 61 Apple analysts — 27 professionals and 34 independents — 31 million iPhones happens to be the dividing line between the two groups.

The average estimate among the pros is 29.54 million and the average among the indies is 31.17 million.

But unlike other categories, where the indies are almost universally bullish and the pros universally cautious, the iPhone numbers are all over the lot, with professionals like Gabelli’s Hendi Susanto (at 34.6 million) and Societe General’s Andy Perkins (33 million) offering some of the highest estimates we’ve seen. At the other extreme, independents like Asymco’s Horace Dediu and Corey Forsberg of the Apple Finance Board offered some of the lowest estimates: 28.5 million apiece.

Our six analysts with the best track record, who usually offer estimates lower than the most optimistic indies but higher than the more cautious pros, came in this quarter well over Blair’s warning line, with an average estimate of 32.1 million.

We’ll find out who was closest to the mark when Apple reports its earnings after the markets close on Tuesday, July 24.

Below the fold: The analysts’ individual estimates, with the pros in blue and the amateurs in green. Note the unusual mixing of the two colors.