iPod shipments for the December quarter may be significantly below expectations, according to analysts Gene Munster and Michael Olson of the research firm Piper Jaffray. The prediction is based on a combination of figures collected from NPD, and the typical breakdown of iPod sales in the quarter for the past three years -- 12 percent in October, 24 percent in November, and 64 percent in December. October and November sales are said to be at least partly influenced by the regular introduction of new iPods, in this case the Touch, Classic and 3G Nano.

Using this formulation, Munster and Olson suggest that 24 to 25 million iPods may have been sold during the December quarter, a drop from the 25 to 26 million predicted when only the October and November NPD data was available. The current Piper unit estimate, meanwhile, is pegged at 23.5 million, below that of The Street's 24.7 million.

Depressed iPod sales may not be as much of an issue however, as when Apple releases its financial results later today, it is expected that Mac sales will exceed predictions, hitting 2.3 million instead of the projected 2.2. iPhone sales have likewise been healthy since the product's debut in June of last year.