I would be very surprised to see that title come out for the PS2. The goal is going to be to try and maximize it's marketable life. The PS2 is winding down, and I believe is "dead" around the middle of 2010. The PS3 however is at the very beginning of it's 10 year life cycle.
You'll almost certainly have to pony up for an Xbox 360 or PS3 if you want to play that on a console.
does somebody know if gta 4 will be available for ps2?

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