How to send SMS with extension number on iphone 1 1?

Take the IPhone XR phone as an example:

1. Open the home page of the mobile phone and click Information to enter, as shown below.

2. Enter the information interface and click New, as shown in the figure below.

3. Enter the new interface and click the recipient, as shown in the figure below.

4. Enter the recipient number or add an address book, as shown in the figure below.

5. After adding the recipient, the default mobile phone card name will appear. Click on the mobile phone card, as shown in the figure below.

6. The option of two cards appears, and switch to the card to be used, as shown in the figure below.

7. After the handover is successful, enter a short message and click Send, as shown in the figure below.