The games are region free. I think any online servers are long gone. There were a few download only games, but now you can only find them on 'Not for resale' store demo cards (or warez). I think all the online games also have 1P mode. A lot of games support local multiplayer via blue tooth, but you'd need 2 N-Gages.
I have no idea about current prices. I grabbed 2 QDs @ $40 when EB/Gamestop had them on clearance years ago.
EDIT: Just searched for the old 'N-Gage Arena' online service, and looks like they still use the N-Gage brand for newer phones. I've only played the earlier line of N-Gage products. Looks like the new N-Gage line is downloadable content only and earlier N-Gage units aren't compatible with new content. They probably should have changed the name... sorry if I caused any confusion.