How does Apple send messages with the secondary number?

1, open the iPhone, click Info 2, click on the upper right corner to write a new message, enter the mobile phone number of the recipient, or click the+at the back to select the recipient 3 from the address book. When editing the short message text, the main number prompt will pop up. If you want to switch to the secondary number, please click this button to switch. 4. If the text message sent by this contact was sent to your main number, but you are now a secondary number. At this point, if you reply directly, it will become a main card message. 5. If you want to send a message with a different card, you need to delete the previous message. If you don't want to delete the previous SMS, you need to use the card-fetching pin and take out the main card before sending SMS with the secondary card. 6. To set the primary and secondary phone numbers of iPhone, you need to enter Settings-Cellular Mobile Network, and then you can see two phone numbers, so that you can determine the primary and secondary phone numbers. This answer was recommended by netizens.