i started playing 3 because i heard the single player campaign has checkpoints. i don't have much interest in multiplayer but it looks like lan support is still available. i have heard on some videos that people still play it in multiplayer by bridging the lan support across the internet.

I saw that ps rewired has a "socom 3 / combined assault" section. i do wonder if just vanilla socom 3 would be playable there because i think combined assault has different maps? at any rate, there were only two people online when i looked at that. it's possible that it picks up on nights/weekends as opposed to 0800 CDT on a thursday.

EDIT: i also bumped into this list, so maybe there are other ways to play: https://ps2online.com/