No hard date for its public release: the official line is "summer" when it will be free for all iPhones (although hobbled on the iPhone EDGE, with no MMS and no stereo Bluetooth) and $9.95 for iPod touches.

Now let's see how long it takes for those beta images to start circulating around. It will pop here when it's available (site is still down as of this writing): Apple Developer Connection.

[iPhone 3.0 OS Guide: Everything You Need to Know]