Definitely no connection relating to SIM. I have the RM-937 L1520 and my time zone ALWAYS defaults to some South American time zone. I live in Toronto, CAN and use a SIM from my carrier. I set it to automatically set and it doesn't change to Eastern Standard (which it should be). I have to manually adjust. On soft resets my date and time and time zone will stick. BUT when I reset using power + vol down the time, date and time zone all are off. This happens 100% of time.