Wandering around E3, you can find no less then 4 different areas to play Phantasy Star Online Episode I & II. One of these doesn't actually allow you to play the game itself, but instead has a cable connecting it to a Game Boy Advance.
On the TV screen, you're given an option to choose one of 3 mini-games from, and based on, other Sega titles. First, you choose either NiGHTS, Puyo Pop, and a Chao Adventure game, and the game transfers data to the GBA. When it's done, you can play those games on the GBA.
While no game cart was inserted, the cable between the two systems was wired into the GBA cart slot, as opposed to the link cable port the GameCube/GBA cable uses. There's been no mention of the neccesity to have a GBA cart as well as PSO, but we'll keep you posted.
Phantasy Star Online Episode I & II is due for release in North America this October. Look for more media soon.