Activision has been thinking about charging for Call of Duty online for a year or so now.
And that might happen with Modern Warfare 3. MW3 is supposed to be an MMO. And if that is true, they could very well charge for online.
But remember. You wouldn't only pay for it on PS3. If Activision charged for online play, you'd pay for it on Xbox Live aswell.
Yes, you would pay to have a Gold Xbox Live membership and an online membership for Activision. Sounds bad doesn't it? As far as i'm considered, Call of Duty is DONE.