It's not quite the App Store, but Ustream's broadcasting app is here on jailbroken iPhones. It joins Qik, which already does the same thing.
Ustream's plan is still to get the app on the official App Store, which would make it much, much more accessible to the general public. The good news is that their latency from streaming to watching is pretty good (about 2-3 seconds), which is live enough to be called live. Not good enough, though, for having a conversation with.
When we tried it over Wi-Fi, the video quality was pretty acceptable for streaming video from a phone. There are a couple short sample videos here. You can actually make out the text if I get in close enough to the screen. What does this say? One, the iPhone 3G's camera is decent enough to take video and the processor is fast enough to process and upload it. Two, we're dying to get this in the App Store so everyone can try.
Another really cool feature is the live poll, which you can activate and have all your viewers vote on. It sends an email to your account address when you close the poll.
The tech is there, so all that's left is for Apple to approve it. You can get it now by jailbreaking.