It has already been announced that Phantasy Star Online 2 will be for the PC in Japan, now they say that they have a Vita version of the online game that will be released in 2013. You will be able to play both versions together.
Unlike the Phantasy Star Universe for the PS2, which had no way to do major updates, PSO2 will be able to have major updates and add-ons due to it being a different platform altogether.
Another addition for the PS Vita players is they will be able to play on both Wi-fi and 3G. When playing the Vita, the Wi-fi allows the users data speed to match that of the PC's. However, the 3G is not the same, though they are planning something different with that.
It has not been verified whether PSO2 will be released for North America or not.