That would be really cool if you could be sitting in an airport with nothing but time to kill thanks to an oh-so-common delay, whip out your iPhone and rent a movie via WiFi for $3 and watch it as much as you want for a month.
x10 lol. That would be pretty amazing. I know M$ is doing that whole deal with online rentals on the 360 but having it on the iPhone would be great. Especially if it dloaded right to it (the phone) i know rates are slow but if you have wifi it will be pretty fast. Although i believe jobs said he would not have wireless syncing so i guess that means no data transfer.
You can choose from 1, 2, hell maybe 10 from your downloads on Apple tv then just ditch them when your sick of them. This would help the issue of small storage space. Downloading from wifi would be out of this world.
I'm thinking this would probably have to be down through your iTunes software when you're synced to a computer. If you're not gonna be able to buy songs on the go, then you sure won't rent movies on the go.