What should I do if there is a prompt message on Apple's mobile phone interface?

1. Install the used SIM card on the iPhone;

2. Make sure that the iPhone is connected to the cellular network;

3. Open the settings application and click Info;

4. In the information panel, turn on the iMessage switch. When the other party also opens iMessage, the message sent is blue.

The specific operation is as follows:

1, click Settings.

2. Click on the information.

3. Turn on the iMessage switch.