According to Gunota:
Gundam SEED goes theatrical UPDATED
Rumors on 2ch said to be from the Sony Music Anime Fes' 06 are that it was announced that there'll be a Gundam SEED movie.
It is known, through a radio commercial for this month's Newtype, that the magazine has "big Gundam SEED news" though early issues don't appear to have come out yet to confirm what exactly that news is.
Edit: Sunrise confirms the rumors, stating this will be the first completely original Gundam feature film since Gundam F91 came out 15 years ago. Mitsuo Fukuda will be the director.
Update 2: Based on people who attended the Anime Fes, Shinn Asuka, Cagalli Yula Atha, Lacus Clyne, Athrun Zara, and Kira Yamato were featured with narration "their path takes us.." to a screen officially announcing the theatrical production. TM Revolution apparently topped off the event by saying "See ya at the movies" to the crowd.