The Simplify Media iPhone application (iTunes link) v1.1 has hit the App Store. As you can see from the video above, with Simplify Media installed on your Mac and on your iPhone or iPod touch, you can stream your home iTunes library to your mobile device wherever you may be. It will supposedly work over EDGE, 3G, or WiFi and promises what might be the holy grail for mobile audio devices -- practically unlimited storage.
To get started you'll need to download the Simplify Media Mac client as well as register for a free account. Then install the iPhone client on your mobile device and your home Mac should show up as a streaming source. In addition to your home machine, you can connect to up to 30 friends also running the cross-platform software.
Simplify Media for Mac is a free download. Only the first 100,000 copies of the iPhone version are free to download, after that it will be $3.99.