The iPad sales number is the one that’s most likely to surprise us in Apple’s Christmas quarter report, which will be released on January 27th. The consensus expectation has recently converged to around 25 million units, with several analysts exhibiting a herd mentality as they seek safety in numbers. As usual, Wall Street analysts are about 2 million units below the indie analysts. But the thing that is fiendishly hard to forecast is what sort of iPads Apple sold during the quarter. This is crucially important, because one of the biggest fears that investors have about Apple concerns its device average sales price (ASP) decline. iPads are more vulnerable to that decline than iPhones, which are heavily subsidized by operators in many markets.