Piper Jaffray said today that Apple’s iTunes Music Store could begin to have a “notable” earnings impact in calendar 2005 and 2006. “We are currently modeling for iTunes revenue to account for 3.6% of revenue in calendar 2006,” the research firm said. Piper Jaffray said iTunes downloads for 2005 could reach 513 million versus the current estimate of 387 million, and 2006 iTunes downloads could reach 1 billion versus the current estimate of 542 million. Piper Jaffray maintains an “outperform” rating and US$100 target price on Apple.