Sony has officially announced on the PlayStation Blog that Uncharted 3's multiplayer is now a free to play game.
Starting today, you can hop on PSN and download the multiplayer game for free and play as long as you like. Once you hit level 15 however your progress will cap unless you choose to unlock it. Sounds like Sony is experimenting with potential future pricing models on the PS4, no?
Here's a graphic that shows the tiers, and there's a bunch more info on the PlayStation Blog about it as well.