What do you mean you've already sent a text message?

SMS is sent through your mobile phone card, which takes up the number of SMS sent by your mobile phone or deducts the fee according to the SMS fee of the operator. IMessage means that Apple devices send messages to each other through traffic or wireless networks, just like WeChat.

Short Message Service (SMS) is a part of Unified Communications Service Plan. Users can directly send or receive text or digital information through mobile phones or other telecommunication terminals. The number of characters that users can receive and send short messages at a time is 160 English, numeric characters or 70 Chinese characters. Short message is a telecommunication service in digital mobile communication system. It is a non-real-time and non-voice data communication service to transmit text or digital short messages through the signaling channel and signaling network of mobile communication system.