My uncle bought a new LG900 a couple weeks ago. He had problem with it so he changed to a different phone. He gave me the LG900 phone. I want to use it but can't activate. The phone screen says "Unregistered SIM" but when I activated it online, I received the message "SIM already registered". My uncle told me that I might need a new SIM card. How do I get a new SIM card?