A new report from Jupiter Research predicts that in the US alone, over 100 million portable MP3 players will be in use by 2011.

The 'US Portable Music Device Forecast, 2006 to 2011' concept report forecasts what the company says will be a "dramatic slowdown" in the sales of MP3 players, followed by steady expansion through 2011.

The report comes as Microsoft prepares to launch its highly-anticipated Zune player on November 14, just weeks after SanDisk and Apple rolled out major upgrades to their MP3 players.

One company that may not feel the predicted slowdown is iPod maker Apple Computers. Jupiter vice president and research director Michael Gartenberg says that Apple's customers have come to expect and support regular product upgrades, making them more frequent buyers.

"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.

The study criticises some MP3-ready mobile phone systems, saying that though the devices will outnumber dedicated MP3 players by 2009, the actual usage of the phones for listening to music is "nascent in the US".

"US mobile phone carriers are underemphasizing or ignoring altogether the necessity of enabling users to 'sideload' existing music collections onto a phone because they can't charge for it," said Jupiter Research vice president and senior analyst David Card, who served as lead analyst for the report.