I dont know how to on PS3, but on 360 you can get into a tenth lobby.
70
Get to rank 70
10 prestige level 70 commander
The highest rank is Prestige 10 at level 70, the emblem is a circle with a skull inside of it.
To finish the campaign 100 percent on modern warfare 2, you have to finish the game on veteran, and collect all the intels. To finish it 100% on multiplayer, you have to get to rank 70, the very last rank. And in the Spec Ops mode, you have to finsih every mission, 3 stars each.
Call of Duty 4 Modern Warfare: Commander: Level 55 Call of Duty World at War: Commander: Level 65 Call of Duty Modern Warfare 2: Commander: Level 70 Call of Duty Black Ops: Commander: Level 50
There are a total of 70 levels (ranks) in Modern Warfare 2 Multiplayer.
10
Level 70 10th prestige
You need to level and complete challenges
You must reach level 70.
There are 70 levels + 10 presiges