So myself and a buddy originally started working re-creating the online servers for SOCOM 1 a few years ago. We ended up getting SOCOM 2 working first and then Socom 1 followed suit.
From there we've been getting most of the first party online games working again and I decided to dip into some PSP games and I have gotten the following games working with the PSP again.

Code:
ATV Off Road Fury Blazin' Trails (On test server)
NBA 07 (On test server)
Gretzky NHL 2k5 (On test server)
NBA (On test server)
NBA 06 (On test server)
Gretzky NHL 06 (On test server)
The PS2 games we support are:
NTSC
SOCOM US Navy Seals
SOCOM II US Navy Seals
SOCOM II Us Navy Seals Beta
Amplitude
Syphon Filter: The Omega Strain
Killzone
My Street
Destruction Derby Arenas
ATV Off Road Fury 2
ATV Off Road Fury 2 Beta
Ratchet and Clank: Up your Arsenal
Frequency

PAL
SOCOM US Navy Seals (AUS)
SOCOM US Navy Seals (EUR)
SOCOM II US Navy Seals (AUS)
SOCOM II US Navy Seals (EU)
Syphon Filter: The Omega Strain
Hardware Online Arena
Ratchet and Clank 3
Killzone Beta

Korean
Hardware Online Arena (Cross compatible with the PAL version.)
SOCOM II US Navy Seals
Syphon Filter: The Omega Strain

Japan
SOCOM 1 US Navy Seals
SOCOM 2 US Navy Seals

To connect you will need a PSP or use jpcsp (unofficial New jpcsp revision 62d49e0)
Create / modify your WiFi connect on the psp and set the DNS to 104.237.9.163

PPSSPP has some experimental infrastructure support which came from the fact that there are some infrastructure games working again.

If anyone is interested we also have a development discord for this project.
PS2 Rewired