Why can Apple mobile phones successfully send messages to each other when there is a network?

Because you have opened imessage, texting between Apple phones is free, and you can't send it without the network. If you want to go with Apple when there is no internet, just tick "SMS" in the message, so you can send them as SMS when the internet is not good. The steps are as follows:

Step 1: Open the main page of the mobile phone and click Settings.

Step 2, click information.

Step 3, turn off the imessage function.

Method of sending information:

Step 1: Open the main page of the mobile phone and click Information.

Step 2, click the plus sign in the upper right corner.

Step 3: Edit the message, select the recipient and click Send.