And how to send text messages with multiple extension numbers.

1. First click the "Edit" icon in the upper right corner of the "SMS" page, as shown in the figure below.

2. Then enter the other person's mobile phone number in the box above or click+to select a contact in the address book.

3. After entering "Mobile Phone Number", the current default "SIM Card" will be displayed, and then click.

4. Then, in the window that opens, select "Auxiliary Number" for the next operation.

5. The "secondary number" displayed on the editing page has been set successfully, and you can use the "secondary number" to send short messages.