If you ignore the fact that iPhones — and for that matter, iPads — are a kind of iPod, then sales of what was once Apple’s (AAPL) biggest moneymaker have been drifting south since Christmas 2008, when they peaked at 22.7 million for the quarter (Apple’s fiscal Q1 2009).

Among the 44 analysts we’ve heard from so far, the consensus is that unit sales for Q1 2012 will come in lower once again — at roughly 13.9 million.

There’s not much air in this category between the average institutional estimate (13.34 million ) and the average independent (14.43 million), although the spread between high and low individual estimates is enormous. The outliers both come independents at the Mac Observer’s Apple Finance Board: Chuck McKenna (at 9 million) and  Alexis Cabot  (18.09 million).

We’ll find out who was closest to the mark Tuesday Jan. 24 at about 4:30 p.m. EST, when the quarterly results hit the business wires. Apple is scheduled to discuss those results in a 5 p.m. conference call with analysts that the company will webcast here.

Below: The estimates we’ve gathered so far and the dates they were submitted, with the independents in green and the institutionals in blue. The rank numbers show how accurate each analyst’s revenue and EPS estimates were over the past four quarters (the lower the better).