The Samsung Galaxy Stellar that the sales staff at the Smyrna, TN store introduced, promoted and sold to me has been a non-functioning device for over twenty-four hours. Although it worked--with problems--before I took it in to the store, after they performed a factory reset, I have only been able to send/receive two phone calls. I personally have no way of knowing just how many calls that I have not received as a result of the "The mobile network will be unavailable until you restart with a valid SIM card inserted" error that I wasn't having before they ran diagnostics. (There IS a valid SIM card in the device.) But not to worry, as a solution, I have to return to the store again today, so they can give me ANOTHER "factory certified" version of the same phone.
It's just my belief, but I've learned that sometimes the cost of a new phone, or some special consideration to a loyal customer of almost two decades will cost a company far less in the long run than the impact of a dissatisfied customer.