HIGH SCHOOL MUSICAL 3 is all systems go - stars Vanessa Hudgens and Ashley Tisdale have signed on for the second sequel. Amid reports Disney bosses wouldn't welcome Hudgens back after naked cameraphone photos of her appeared online, the pretty brunette was the first castmate to sign up for the film, closely followed by Tisdale. The news follows a hold-out by the leading castmates, but now all of them are expected to return for High School Musical 3. Hudgens' real-life boyfriend Zac Efron is expected to sign on for the third film and a publicist representing Corbin Bleu and Monique Coleman tell Us Weekly magazine the pair is in final negotiations to join the movie, which will be the first High School Musical to have a national theatrical release. The first two movies broke TV records when they aired in America. Shooting on the third film is scheduled to begin in January (08).