[Nextgrid]

Number assignment is handled at the network level. I have the exact functionality you speak of (single number to multiple devices) on my company's good old physical SIMs.

Phones & SIMs don't even know nor care about their own number. The SIM has a field for that but in fact it's often left empty (iOS devices discover their own number by texting a known Apple number and getting the response via the Internet, they'll then populate this field out of courtesy but it's not necessary for functionality).

When a call comes in, the carrier decides which SIM it should be routed to. When a SIM makes an outbound call, the carrier decides which number to set as caller ID.

The functionality you speak of has nothing to do with SIM vs eSIM, it's about carriers having to actually innovate and do some engineering. Their current oligopoly means there's no commercial pressure for them to do so, and there's no reason why they would suddenly do this with the switch to eSIMs.

[newsbinator]

> iOS devices discover their own number by texting a known Apple number and getting the response via the Internet, they'll then populate this field out of courtesy but it's not necessary for functionality

TIL! Is that why in some countries and some SIM cards my iPhone can automatically report its own phone number (when I look at my own profile under 'Contacts') and in some countries it doesn't do that?

[Nextgrid]

Yes!

Carriers who assign numbers to SIMs in advance could set that field directly. Others, either because they don't assign a number at the time of the SIM manufacture/personalization or just because they can't be bothered as it's not functionally necessary will leave it blank - in that case from my experience iPhones will populate the field with the number they get back from the iMessage & FaceTime provisioning step but again that's not actually necessary for functionality. The field is also user-editable in Settings -> Phone if you wish.

[seti0Cha]

Nextgrid, you're all over this topic providing high quality answers. Just wanted to say thanks for helping justify my still reading HN comments.