How do you unlock radar in COD4: MW Online Deathmatch?

May be...

I saw a hint on a load screen about radar. Is it just telling me to use the regular one or can you unlock another?

Once you have a three kill streak. You have the ability to call in a U.A.V. This will mark all the enemy players as red dots on the compass. To use it press the right arrow on the d-pad of your PS3 controller.

you just need a 3 kill streak for it a 5 kill streak for a airstrike and a seven kill streak for an helicopter