With the upcoming new iPhone, I'm going to make the jump up from my very old model (iPhone 8) to a 15 when they knock the price of the 15 down a notch or two upon release of the 16. With that will come eSIM capabilities. So, I feel the need to dive in with a basic question or two.

My current phone (the 8) uses a hard SIM with T-Mo. From experience setting up a relative's iPhone 13 (or 14), I know that during the upgrade, T-Mo will say "bye to your old phone and SIM card, hello to your new phone and eSim". OK, easy. Touch wood.

Now, I maintain a S. African (Vodacom) number on an iPhone 6 with a hard sim card. I use it in SA (duh!) and when in the USA, only turn it on, make a voice call or two (over either the Tmo or AT&T roaming voice network) and send and receive a few WhatsApps over wifi to keep the phone and number "alive" through regular usage.

If I'm understanding this new "multiple eSim" support on latest IPhones, it seems I can add the Voda number into the new phone as my "second" SIM (via eSIM). Side Q: if anyone has done this via Vodacom SA (particularly while NOT in SA) I'd appreciate tips.

But, here's my Qs. How do I choose which "number" (e.g. my US Tmo number or my Voda SA number) to "use" to make a call over the voice network? When I press the green "phone" button on the iPhone dialpad - do I get a pop-up that says s/s "Why SIM do you want to use?"

And, similarly - for data - I keep data roaming off on my SA iPhone when in the USA. How do I "set" the phone to choose the right number/SIM to send and receive data over the cell network? Can I keep the TMo data "on" all the time and toggle the SA Voda data "on, off, roaming"?

Thanks all. If this works, I may just by a EU SIM and as AUS one for my EU and AUS friends to be able to "dial local" to me.