I just read this thread http://forums.macrumors.com/showthread.php?p=11038813#post11038813 which was sort of helpful but didn't answer all of my questions. I've bought my daughter an iPhone for Christmas. I want to get some things set up today, her email, Find My iPhone, etc. and update the OS to 4.2. The SIM I have for her is not active as she is still using her old non-sim/CDMA phone and I won't be transferring her account to the SIM until Christmas day. If I want to be able to update the OS and get things set up on the phone, can I do so with her new SIM that doesn't have a phone # attached to it yet? or can I do so with my iPhone SIM? The other thread said *not* to update the OS on the phone, why is that? That's one of the reasons why I am doing this. Oh, her phone will be locked to the carrier where mine is factory unlocked if there's any reason that will make a difference.