Forty percent of UK mobile phone users own a music phone. And 31 percent of US users who use both a music player and a phone selected their phone as their primary music device, according to the research by M:Metrics. The Crave site of C|Net UK report the results.

"Almost a third of January phone sales in the US were music phones, so we can expect more and more people will listen to music primarily on their phones," the report said.

To support the idea that customers are moving more and more to music enabled phones, C|Net, in turn, looked at the history of PDAs and noted: "PDAs have already been crushed by smart phones and the same thing looks to be happening with standalone MP3 players, particularly the smaller flash ones -- a theory supported by Apple’s recent entry into the world of music phones."

Some continue to argue that there is no substitute for a really good stand alone device. In addition, current battery technology places a real strain on music-enabled phones, and that may be slowing the rate of adoption.

In all the other technologies that customers tend to engage in, taking photos, surfing the Web, and navigators, the stand alone units still do it better. So far.

But the interesting question C|Net posed is how long it’s going to take before "all you need is a mobile phone." For some, the answer may be, not long at all.