Now you know to advise people to look into that question before the install/find an installer that can guarantee it. If the thing can't easily have cell function disabled (e.g. by pulling a readily accessible card), then advise people to stay away from enphase.

Enphase required the cell connection when I checked a couple years ago. Sol-Ark makes a solid hybrid inverter and allows offline operation.

After I bought out our panels, I found the Enphase modem and disconnected it. It was a USB box connected to the monitoring unit, the monitoring unit has other networking options, and it's mine anyway.