A 2nd rumoured mobile game has been announced, Seiken Densetsu: Friends of Mana.
http://www.square-enix.co.jp/mobile/seiken/fom/
From what I can tell on the page, it will be released Oct 2006 in Japan, and takes place 10 years prior to Legend of Mana.
For those interested, the first mobile game page is here:
http://www.square-enix.co.jp/mobile/seiken/sdff/