Errr... By killing people and getting experience points?
Sadly no.
Yes, there is online multiplayer on Call of Duty 4: Modern Warfare.
In Call of Duty 4: Modern Warfare, the M14 rifle is unlocked at Level 46 in multiplayer.
U go to multiplayer if no multiplayer u beat
10 prestige level 70 commander
Call of Duty World at War, Modern Warfare, Modern Warfare 2, Black Ops, and Modern Warfare 3 all have online multiplayer.
Yes You Can
Unfortunately no, you can't play multiplayer on Call of Duty Modern Warfare 1 or on Call of Duty Modern Warfare 2 on the same screen. But on Call of Duty Modern Warfare 3 and Call of Duty Modern Warfare Black Ops you can play multiplayer on the same screen. There is an new Call of Duty Black Ops 2 coming out soon though, so I expect that to also have that feature, since its newer.
There are a total of 70 levels (ranks) in Modern Warfare 2 Multiplayer.
No you can't.
This is quite a vague question, but if, by chance, you are asking at which level the G3 unlocks in Call of Duty 4: Modern Warfare's multiplayer, the answer is at level 25.
Yeah there is! I know there is for the PC but i am not to sure for the PS3 olr XBOX. Have a look on the net!