There is a FREE SERVER for Ragnarok Online. I think it's the ORO server.
I am not 100% sure on details connect onto this server. HOWEVER if you go on the
Ragnaholics Forum, you will get details there.
Be warned that the server is UNSTABLE and you can loose character (or time) on your characters.
As for
Ragnarok Online as game. At first I found it was cute, but after about 6 month of playing (roughly about 3 hours per day) reaching level 50, i still did not feel that I progressed anywhere. I found the game rather repeative.
Ragnarok does allow you to have 3 chacter per server. However there is not much you can do to change professions once the character has been created.
I stopped playing Ragnarok Online about 6 weeks ago.
Since then, I have been playing Star Wars Galaxies, and never looked back.
Over all, if you are wanting a "GOOD" mmolrpg to play, then expect to pay for it. Otherwise, look around for any BETA TESTING servers.
I have seen some other games (forgotten the name now) where you can play all you want for free, but your character has some heavy restrictions against him.