Some wisdom from slashfilm:

Originally there were rumors that the first trailer for Wes Anderson’s animated Fantastic Mr. Fox would be attached to Ice Age: Dawn of the Dinosaurs. As you’ve probably figured out by now, the trailer was not attached. So right now, I have no idea when the trailer will hit. Anyone have any ideas? The movie isn’t scheduled to hit theaters until mid-November so there is still a lot of time. The next possible sighting would be Fox’s hybrid Aliens in the Attic on July 31st.

The kids over at IMDB similarly wonder out loud:

I think the best bets are Harry Potter (highly unlikely), G-Force (also unlikely), and Aliens in the Attic (probably the best bet seeing as how it’s the same studio.)