i cant tell you the exact number as not everyone has online access and the number of purchases is ever expanding,
however judging by the leaderboards from my Xbox 360 the bottom player is rank 6,330,421 at least that was the current count on the 21st December at 7: 20pm gmt
Between 6 and 13 million per system.
The figure seems high. They have not sold that many games for the PS3 and many people that have the game no longer play it online or offline. I would be very surprised and amazed if even a million different people played it a month on all the systems combined. Under most played games at Gamespot they show three times the hours for Call of Duty Black Ops as Call of Duty Modern Warfare 2
i dont no!
You obviously have to pay for the game, but there are no fees for playing online.
In my opinion, you should hold on to the other games if you can, but more people will be playing on the newer games online.
Yes as long as its compatible with Modern Warfare 2
No
Mostly on the campaign no but if your on multi or online playing you can be on Search and Destroy.
Yes
On PS3 it is, you'll have to pay for xbox live when you're playing on xbox probably
Yes, there is online multiplayer on Call of Duty 4: Modern Warfare.
there is none
Just go online and play a game mode... you'll be playing with multiple players.
no but your just going to have to look on modern warfare 2 online