I have a Nokia 6102i, S/N 352735019840110. Provider is Cingular in the US. I would like to use the phone in Australia, with the original SIM card, as it connects to the system fine. It won't make or receive calls. If I cannot use the orginal SIM card, I would purchase a local SIM card, then reinstall the original for the US. Will this void my warranty, or contract with Cingular? Can I relock the phone before I return to the US, and be OK? Thanks in advance.