After some delay here is the stable version 0.5.2 which was released by the openttd dev team at late May, now ported to PSP, looks like they will release 0.5.3 soon, so i hope to release the PSP port of it as soon as possible.
Currently the port implements all the game features, such as sound, music, newgrf, tt fonts, wireless multiplayer, etc... so feel free to let me know any bugs you find to fix them on future versions.
This new version includes some sound and suspend bug fixes.
Current ChangeLog:
Code updated to 0.5.2 to be able to play on latest online servers
Game crash when suspending fixed
Native PSP sound effects driver developed instead of using SDL_mixer