NB-IoT and LTE-M are cellular LPWA networks specialised for IoT use cases. They are built on LTE (4G) technology and will be continued onto the fifth generation (5G) cellular network.
NB-IoT is specially tailored for use cases where battery life and wide area coverage is crucial. It is designed for devices that send small amounts of data and can enter sleep cycles between communication windows.
LTE-M allows for higher throughput than NB-IoT, while still enabling power saving functionality and enhanced coverage. The LTE-M network also allows for voice over LTE (VoLTE), which makes it ideal for use cases where you need to send sound messages.