Bought a fully loaded IPP 12" last week. Have not yet turned on my iPad's cellular service. Every time I get ready to, I have problems with the SIM card. Usually it's that the CSN number doesn't show up in Preferences, General, About. A few times on rebooting the IPP I got "SIM card not found." I've removed the card several times and cleaned it for dust. Isn't the CSN number supposed to show up ALL the time, even when out of range of cell tower service? I called both Apple and AT&T and no one seems to know. I'm really worried that if I start the service, then I'll find out that the SIMcard is defective. NOW is the time to return the unit, or try to get a replacement SIM card from Apple. Does anyone understand this stuff? Googling is getting me nowhere.