Send text messages to each other. Can anyone know if they can't locate it?

Short message service (SMS) is a part of unified communication 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.