What if I can't answer the phone and then send a text message?

Have you ever turned on imessage, Apple's network short message tool, to send short messages between ios devices and macos through the network? If you are a mobile 2g user, if you send a short message to a user who has also enabled iMessage, the iphone will send a network short message first by default, but it will take a long time and may even be unsuccessful because of the slow mobile gprs. Therefore, if you are not a 3g user of China Unicom or Telecom, you'd better not open imessage. Or turn off cellular data when sending SMS, and let iPhone automatically send ordinary SMS when it thinks there is no network connection.