Multiple old questions (here, here, here, and here) document that even when mobile data is switched off, mobile data still gets used as part of 4G voice service. I'm looking for up to date information (e.g. possibly relating to 5G, eSIMs, latest Android version, retirement of 3G, etc.) to see if the following scenario is possible without rooting my phone:
- Home SIM active for SMS (but not MMS)
- Home SIM active for voice calls (this is not essential to me)
- eSIM for ALL mobile data used while travelling
Why am I so keen on this? The ability to receive SMS codes is sometimes needed to verify oneself to a service. (Yes, I know it is not as good as other alternatives.) As of 2023 eSIMs provide very cost effective data service almost anywhere in the world, while international data roaming charges from one's home carrier can be exorbitant (e.g. $10/MB for me). At those rates, tiny amounts of unexpected data use can add up fast.
Doing all of the following is NOT sufficient to avoid use of mobile data:
- Turn off mobile data AND turn off data roaming for the home SIM
- Send zero text messages and make/receive zero voice calls
- Turn off MMS for the home SIM
- Turn off "Data during calls"
- Are any new strategies/settings available or in development?
- Does 5G have the same problem as 4G - using data to establish itself on the roaming voice network?
- Would setting preferred SMS to my home SIM, but voice calls to a data-only eSIM be possible?
- I would consider moving to iPhone: Is this an Android-specific issue?