According to this IGN report, a feature-length movie of Professor Layton's in the works and planned for a 2010 release in Japan.

Titled Professor Layton The First Movie - points if you can spot parallels with any other Nintendo handheld franchises - the film will feature the same voice cast as the game, with Yo Oizumi as Layton and Maki Horikita as Ruke.

More through there.