According to GCAdvanced, there is going to be a Phantasy Star Online DS.
Here is the article they posted:
Top SEGA franchises on Nintendo DS? We caught wind of some unofficially announced titles that you can expect. In what is purely speculation at this point, a reliable source has passed along the wonderful news of new SEGA titles planned for Nintendo DS.
Whether the titles listed below are currently in development or just in planning stages, you can expect all of these games to make an appearance in some way, shape, or form:
While those are the previously announced and/or rumored titles, we are pleased to pass along the great news of even more Nintendo DS support from SEGA:
Phantasy Star Online DS (tentative title), is said to include both wireless and/or WiFi play, voice command options with the built in microphone and of course touch screen options.
The rumored title, code named, "Project Rub," is said to be an entirely new and original project from SEGA for Nintendo DS, with no other information known. Perhaps from the suggested code-name, the touch screen will play a large part in the games creation.
I will keep you guys up-to-date on this news.