Well you could play used game because the info is not saved on the game itself but on the server and ur network configurations are saved on your memory card. You would obviously have to start a new account. However, on the front of the Instruction manual there is an account key. I'm not sure if this account key is your first original account to get the 30-day free trial or if it is required all the time for that particular disc.
I think if it is the original account key to start the 30-day free trial, after it has expired u can just buy gamecards with new keys.
But in all honesty, I don't know.