What should I do if my iPhone 4s can make calls but cannot receive or send text messages?

Troubleshooting when iPhone cannot send text messages:

1. Make sure the signal is normal and turn off airplane mode.

2. Check whether the SIM card status is normal.

3. Check whether the send button is bright and clickable.

4. If you cannot click send after entering text, the "Send" button will still be gray and cannot be clicked. Please go to Settings > SMS > turn off "Show subject bar".

5. If you are texting multiple people and entering the numbers manually, make sure you press line feed and not spaces to separate each number.

6. If you can receive but cannot send text messages, after the above problems are eliminated, you can use the internal command method to edit the SMS center number:

Set the SMS center number: Dial *5005*7672 on iPhone *+86 SMS center number#;

Delete SMS center number: Dial ##5005*7672# on iPhone.

To check the set SMS center number: Dial *#5005*7672# on your iPhone.

When using internal commands, use the delete command first and then set the SMS center number.