As of two minutes ago, it appears you can now buy music from iTunes from your iPhone over EDGE and 3G, not just Wi-Fi.
Even better: all the music in the store appears to be DRM-free now [emphasis added]. I’m guessing Phil Schiller will announce it later on in the keynote. Maybe this is the “one more thing”?
[From Daring Fireball Linked List: DRM-Free Music at iTunes Store]