I'm talking about two different cases here. First, in a case closer to the current world, I'm just suggesting that disabling the cell modem should power it off

I'm talking about two different cases here. First, in a case closer to the current world, I'm just suggesting that disabling the cell modem should power it off so it can't do any kind of location or tracking. Second, in a more ideal world, the concept of "data connection" would be entirely separate from any identity attached to a phone or text message, and you could handle the latter via whatever connection you have, whether a cell data connection or wifi or something else.