Yes, but recently news has arisen that the release date has been changed to something akin to "indefinite."
the-ethos' bbs, babelfish translation of release dates from a recent issue of Famitsu
31.08.05 - Namco communicates that the game of roles Xenosaga DS was shifted on indefinite time in Japan. Release: TBA
Also according to some talk on the-ethos it doesn't look like XS3 made it into Namco's TGS line-up, or at least they haven't mentioned it yet (so far the only information about it was leaked by Voyager's seiyuu, which basically just said that he (Koji Tsujitani) will be voicing Voyager in the game). The details on DS are sketchy because I've seen contradictory information posted in various places (some places have it listed with Namco's line-up, others don't, I haven't found any conclusive evidence of one being more true than the other yet so I'm not entirely sure).