Phineas and Ferb finally discover that their pet platypus, Perry, is a secret agent who battles the forces of evil almost every day. The boys team up with Perry on an adventure through a parallel universe where they must ultimately thwart the disastrous plans of a even bigger threat than dimwitted Dr. Doofenshmirtz: a parallel Doofenshmirtz, who, unlike his counterpart, is a truly evil genius with no goofy side or soft spot.
Dialogue for the movie began recording the week of April 26, 2010.
Preliminary storyboards for the special, including the opening song "Everything's Better with Perry," were shown at Comic-Con on July 25th, 2010. 
A brief teaser trailer for this film was on The Sorcerer's Apprentice DVD. The trailer did not have any new footage nor any new information on the plot, not either it or Asia trailer teaser. 
The original/full title for this movie is called Phineas and Ferb: Across the 2nd Dimension In Ferbulous 2D.
Images for the Original Plot have been shown on the Disney Channel Asia's 2011 Sneak Peek; however, these were not confirmed images.
Despite being the longest feature of Phineas and Ferb so far, it only has 7 songs, tying with "Wizard of Odd", "Phineas and Ferb Summer Belongs to You!", and "Phineas and Ferb Christmas Vacation!" if What Does He Want? is not counted.
A video game has been announced and is being released for Wii, PS3, and the Nintendo DS.
Movie description from the Amazon press release: 
When Phineas and Ferb accidentally help the evil Dr. Doofenshmirtz complete his latest creation that will finally take control of the Tri-State Area, they get zapped into a new dimension, where they meet their alternate selves! In this new dimension, Dr. Doofenshmirtz is the leader of the Tri-State Area, and even worse—summer vacation doesn't exist! Will Phineas and Ferb figure out a way to get back to Danville, or will they be stuck in this alternate dimension forever?