Hello @Raygon!
Welcome to the AT&T Community Forums! I will be happy to help you register your new account online.
If you have already activated your device, all you need to do is visit our website to create an AT&T ID and password using your phone number. Once you have access to your MyAT&T, the account information will display.
We offer a couple of options to get new SIM cards free of charge: you can order it online through this link, which usually takes two calendar days, excluding Sundays, to arrive. For immediate assistance, you can take the device to a local AT&T corporate store and receive your new SIM card the same day.
I hope this information helps. Have a wonderful weekend and Happy New Year!
Anabel, AT&T Community Specialist