ahmed_b BO2 has many servers and a decent player count. MW3 has a few servers but I rarely find any people playing it. If you see a server with 16 players, its Shakin trickshot server and those 16 players are all bots

Whenever I choose a calling card, exit the game and open it again, I see that my calling card disappears. Is there a way to solve this or we can't use calling cards at all?

Are you on Windows 7?

I've seen a tutorial in Bo2 modding page on this forum to unlock diamond camo and others. Check it out.