This is just a preview, not the release. I expect the software release to be simultaneous with the hardware release, which Tim Cook has been hinting will be in June.
As with the iPhone 3G and iPhone OS 2.0, they're likely to release exclusively on the new device first before making the update available to older generations. There will probably also be some hardware-based features exclusive to iPhone 2009 to incentivize paying for a refresh.
As with the iPhone 3G and iPhone OS 2.0, they're likely to release exclusively on the new device first before making the update available to older generations. There will probably also be some hardware-based features exclusive to iPhone 2009 to incentivize paying for a refresh.