Very few MVNOs like Straight Talk offer official nano SIMs for sale. You (or someone else) make them by cutting down a larger SIM, and that can be imperfect. Officially nano SIMs are also slightly thinner than other SIM sizes, so you have to carefully sand them down although many don't do that and find things work OK. I purchased a NET10 nano SIM from a reseller and have had similar problems although sometimes a reboot fixes it and sometimes a single reinsert of the SIM has fixed the problem (a couple times it's taken several tries). Until I run the phone using an official nano SIM I'm reluctant to say my phone has a problem. Given the new ATT family plan pricing & per line $100 incentive, we'll probably be moving there sooner than I was planning, and ATT can supply a real nano SIM.