There is no demo for Call of Duty: Modern Warfare 3.
A Demo will not be out
No
There is not supposed to be a demo
Never
It is not necessary.
No there is not
it comes out when it comes out!
There's not supposed to be one
Download the turrent or buy the game
The game is low priced after over 3 years since it's release, but I don't know if a demo was ever available for any of the platforms.
Modern warfare 3 is better