There’s a reason why hardware switch for wifi, Bluetooth, microphone and camera on some Linux phones exist, same for the physical SIM card. For physical sim, when it’s taken out, the phone has no way to connect to any tower except for sos depending on country. For esim however, you can turn it off in software, but there’s nothing preventing the OS to connect to surrounding tower every so often to check stuff and whatnot. Yes, esim allows Apple Watch cellular exist, but I also believe removing SIM card tray comes with its own cost. We just don’t know exactly what it is.
Id guess current esim provisioning process prevents cash esim from being a thing, since details must be downloaded from certain carrier somehow during activation, rather than information being stored on physical SIM card, carrier already know enough of your information to activate the network for you.
But you can also delete the eSIM and it will be gone. If you are paranoid enough to think iOS will still keep the eSIM profile after deletion and even use it then you should also be paranoid enough to think iOS will also auto connect to any open WiFi network and transmit as much data as it needs.
Same for Bluetooth too. Maybe Apple has it coded in iOS to transfer data to other surrounding iPhones via AirDrop to use their cellular connection to leak your data. I mean that’s how Find My network works, no?
Also what stops the phone from reporting that the physical SIM is still inserted. The iPhone already knows the data it needs to connect to said tower. Not like the tower can check if the SIM is physically inserted or not.
eSIM changes nothing. It is the very same tech. It is basically a profile with the very basic info about said carrier and their preferred roaming partners and ICCID. It is literally the same data stored on a physical SIM card.
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There is nothing stopping a carrier from offering “cash only” prepaid eSIM card except it just not wanting to. My carrier already issues prepaid eSIMs. eSIMs are no different from a physical SIM.
It just that eSIM is not a necessity and it is exclusive to high end phones so your carrier wants to push you to postpaid since it means more profits to them and a guaranteed monthly payment.