According to this Eurogamer piece, The Agency lead designer Hal Milton has confirmed that the MMO won't include cross-platform play.
The spy game's in development at SOE for both PS3 and PC. Milton dropped the bombshell at the company's annual Fan Faire in Las Vegas.
"A couple of members of our team gained a lot of experience working on Shadowrun, and no matter how well you fine-tune it, you end up with a player-base that's polarised," he said.
More through the link. No date as yet.