Need assistance in configuring primary SIM for calls and SMS on iPhone

You may be aware the there is a difference between "Last Used" and "Always Use"

if you have selected a Line for a Contact, Say Line B as "Always Use"

and If that contact sends you a text using Line A then if you reply to that contact using the received message in the Message App as a continuation of the conversation then the Contact will be assigned as "Last Used"

Always start a conversation from the Contacts App if you want to keep Business and Personal lines separate.

If you start the conversation from the old thread then you cannot change it. Start a new conversation from Contacts App. Here you can change the number as well as the Line. As shown in the GIF below

yugal68 wrote:

I've encountered a challenge where I want to ensure that whenever I initiate a call or send an SMS, it always uses my primary SIM card. Unfortunately, I have not been able to find a solution for this matter through Apple's customer support. I find it surprising that Apple, known for its user-friendly features, does not seem to have a straightforward solution for this particular scenario.

However, the feature on an iPhone is as follows based on the way you are trying to call.

Watch the GIF below to change the Voice line. This has to be done each time you receive a call and want to call back from another line other than through which it was received.

Alternatively, you may change the Voice line to be used under Contacts. And dial using contacts and not using the Recent call list.

While making a fresh call using dial pad.

See the pic below, which is self-explanatory.

You can use Dual SIM by using a physical SIM and an eSIM. iPhone 13 models and later also support two active eSIMs. iPhone models without a ...

Using Dual SIM with an eSIM

Yes