For all the effort pouring into the battle for downloadable music for mobile devices, streamed personal radio has crept up quietly in the meantime, driven by two different factors : the emergence of 3G mobile devices and networks and growth in Web-based personal radio such as Last.FM largely outside the US and Pandora and like services inside the US.

Now Vodafone is pushing a new service out in many of its markets in coming months, Radio DJ, based on a Sony-run service, Streamman, developed for Finnish operator TeliaSonera. All of these personal radio services are based on the principal of starting with a wide pool of music you like based on some basic criteria (for Last.FM, based on your digital listening habits for example), and allow you to select "like" or "don't like" as you hear them in order to narrow the mix down.

Proponents of streamed personal radio for both fixed and mobile environments tout the social aspect of many of these services, which in some cases allow users to connect profiles with friends, thus broadening the field of music they hear based on others's tastes. Sony's role in Radio DJ and Streamman are not surprising as content companies need to keep finding new channels as old media loses strength and share to new media.

According to the International Herald Tribune, Vodafone starting Radio DJ without getting all labels on board first. While this may be risky, remember that iTunes pushed the boat out without everyone on board either. Once it showed momentum, that changed. With Vodafone's footprint in 20 markets, it too may be able to gather the critical mass neccesary to grow the service.