There is a beta xcom for the pocket pc, made by some guys in eastern europe (I think), I tried it, and is almost carbon copy of the original xcom. They have not implemented touch screen capabilities, and is a little hard to play because you can't use a mouse
I think a port from that version to DS won't be that hard to come with, they have the source code and the processors aren't that different right? (I'm completely ignorant about the technical CPU specifications of the DS)