Simplify Media - one of the most popular and innovative 'jailbreak' apps for the iPhone - has gone legit and appeared as an official application, allowing people to stream their music (and their friends' too) to their handset.
Simply Media allows you to set up an account that makes your music available to you via streaming (as long as your PC or Mac is on and connected to the web of course).
An install and a free account with Simply Media is all that's required, and you can also add up to 30 friends' libraries as well.
Once up and running you can browse by playlist or album, and you can also get album art and artist bios.
There's a fair amount of surprise floating up that Apple allowed the app to make it through, and whilst the first 100k downloads are free, it could soon cost a pretty penny to install the service.
In other words, if you like the concept, probably best to get it whilst it's hot.