Sonic Team leader Yuji Naka revealed at Game Jam that Phantasy Star Online Version 2 will be slightly delayed in Japan. It was due to release on May 17, but will instead launch at the end of the month, May 31.
The reason for the delay, according to PSO World, is to improve the game's anti-cheating and security measures. There's no word on a US or European release date, but keep checking in for up to the minute updates!
Source: PSO World