If you have an iPhone 4 why don't you just test it out?
They won't. You will have to bring it into iMovie and transcode it to 960x540. The Apple TV cannot handle 30fps at 720p.
Video formats supported
H.264 and protected H.264 (from iTunes Store): Up to 5 Mbps, Progressive Main Profile (CAVLC) with AAC-LC audio up to 160 Kbps (maximum resolution: 1280 by 720 pixels at 24 fps, 960 by 540 pixels at 30 fps) in .m4v, .mp4, and .mov file formats
iTunes Store purchased video: 320 by 240 pixels, 640 by 480 pixels, 720 by 480 pixels (anamorphic), or high-definition 720p
MPEG-4: Up to 3 Mbps, Simple Profile with AAC-LC audio up to 160 Kbps (maximum resolution: 720 by 432 pixels at 30 fps) in .m4v, .mp4, and .mov file formats
http://www.apple.com/appletv/specs.html
I'll bet there are different recording options.
The new iPhone 4 has a medium quality 540p export option that's compatible with Apple TV. Not HD, but close enough for most people.
Hopefully, we'll get a new Apple TV in the fall or at least a software update to support 30 fps.
Not sure, but iPhone 4 might allow you to record at 24fps. If so, the video would play on the AppleTV as easily as you want. I don't get my iPhone until 7/2, so I can't tell you for sure.
Let's pretend that there is no Apple TV of the Future that will support 720p/30. Can you tell me what product I can purchase right now that will allow me to watch my beautiful 720p/30 HD iP4 video on my 1080p LCD HDTV?
The fact that iPhone 4's 720p video is too much for the current ATV should tell you the ATV to this point truly has been a "hobby." I expect the OP's wishes to come true when the revised ATV is released in it's non-hobby version, whenever that may be.
It would be backwards for Apple to provide a 24fps option on iPhone 4, just to accommodate a device that they've never taken seriously in the first place.