SMS (Short Message Service)
Updated
SMS carries short messages of up to 160 characters of 7-bit text, or 140 bytes, between devices and applications. It is specified in 3GPP TS 23.040. On LTE-M and NB-IoT, SMS can travel over the network signalling, without a data session.
In practice
IoT devices use SMS to receive configuration commands or a wake-up message. Check that the SIM, the network and the device all support SMS: some IoT offers are data only.