The next Phantasy Star game has been announced. This one is Phantasy Star 0 (that's a zero) for Nintendo DS. Here's the official site:
http://phantasystar.sega.jp/pszero/
Don't get your hopes up, though - this may not be an addition to the classics. As you'll see from the site, it borrows a lot from Phantasy Star Online. It has similar races and classes, a close battle system, and so on. Very little has been revealed about the story so far though, so perhaps this will be a connection between Online and the classics. We'll have to wait and see as more info is released.