Jupiter Research predicts the iPod's dominance of the MP3 player market will be unthreatened for at least the next year and a half. What's more, the research firm says the digital music player market will expand from 37 million users this year to 100 million users in 2011.

Michael Gartenberg, vice president and research director at Jupiter Research, said that Apple shows no signs of losing momentum, thanks to its conditioning of customers to expect and adopt regular upgrades.

"Despite the coming of Zune, the return of closed-loop digital music service-device combinations, and music phones on the horizon, the iPod should not lose significant market share in the next 12 to 18 months," said Gartenberg.

Jupiter Research says mobile phones capable of playing MP3-quality songs present the biggest growing threat to digital music players - the number of phones that fit that bill will surpass music devices in quantity by 2009, the firm reports.

David Card, who led the analysis in the report, calls impulse over-the-air music purchases "a tough challenge" both for wireless devices and phones thanks to issues with infrastructure, compatibility, pricing and user interfaces.

"US mobile phone carriers are underemphasising or ignoring altogether the necessity of enabling users to 'sideload' existing music collections onto a phone because they can't charge for it," said Card.