Apple will have sold 1.365bn songs through the iTunes Music Store by the end of 2006, investment house Piper Jaffray calculates.

According to a note send by PJ analyst Gene Munster to investors this week, relayed to the rest of the world by iLounge.com, that's 55.6 per cent more than the company had previously forecast.

The revenue realised will account for five per cent of Apple's sales next year, Munster writes.

His reckoning works along the following lines: “Assuming 133m iTunes downloads in the June quarter and applying that across the reported 6.2m iPod shipments, Apple is averaging 6.1 iTunes downloads per iPod - based on the entire iPod estimated installed base through June 2005. If we apply this 6.1x ratio to our cumulative iPod installed base estimates through 2006, iTunes downloads for 2006 would be 1.365bn."

The Register's back-of-an-envelope estimates based on the Apple's iTunes sales announcements to date suggest ITMS will sell just under 1.12bn songs during 2006 for a grand total of 2bn songs through to mid-January 2007. It should pass the billion-song mark February/March 2006, a few months after we previously forecast, but still an impressive growth rate.

Our figures assume no sales from iTunes Japan, which is clearly ridiculous, even had the Japanese store not proved as successful as it has. We look forward to Apple's next iTunes sales announcement to adjust our model accordingly. ®