I know this is an old post but I thought I might as well throw this out there.
Phantasy Star Online: Blue Burst can be found and played on a private server. I won't give details as how to find the server (google knows all).
http://http://en.wikipedia.org/wiki/Phantasy_Star_OnlineIt's a pretty old and limited game though it still has a lot of players on it (200+ when I looked a few months ago).
Apart from that, if your son has a Nintendo DS then a new version is due out in December called Phantasy Star Zero, looks quite good for a DS game. No subscription of course.
Exteel is more of a behind-view shooter but it's alright. It's a scam in a way though. You have to pay money into the game for good items/weapons.
http://http://www.exteel.com/us/I enjoyed it for a while.