The two low volume cellular technologies for IoT are CATM and NB-IoT. Both technologies are used for transmitting limited amounts of data over the cellular network. Both of these technologies ride on the cellular operators LTE network so coverage when fully deployed will be similar to the coverage you get on your cell phone. Both of these technologies have been predicted to explode in terms of the number of devices being placed on the network. Unfortunately, the uptake has been a lot slower than most had hoped. More and more, the number of devices appearing on the networks is increasing so we're starting to see that growth but it is still not to a point where we'd like to see it.
That being said, for higher bandwidth needs, devices will use CAT-1 or higher. For the low volume needs, CATM is a very viable technology. Several mobile chipsets exist from providers like Qualcomm, Sequans, Mediatek, and others. Module providers then take these cellular baseband modems and build modules to be used in end devices. Some of the key module providers include Quectel, uBlox, Telit, Nordic, Sequans, Gemalto, and others.
CATM can be used for applications that require up to a maximum of 1Mbps speeds and uses a bandwidth of 1.4Mhz. NB-IoT, on the other hand, uses speeds from 20 (UL) - 60 (DL) kbps, using a bandwidth of 200kHz. If you're application is to track stationary items that only require the transmission of a very minimum amount of data per day, the NB-IoT may be the technology for you. NB-IoT is not meant for mobile applications. If your tracking asset that moves and you need to know where it is at all times, then CATM is the better solution.
NB-IoT should be the cheaper solution to implement. The components will be slightly cheaper than CATM and the operators connectivity plans should also be cheaper than CATM.
The current issue with NB-IoT is its availability. NB-IoT is dominant in the Asian markets where AT&T and Verizon deployed CATM first and are now making NB-IoT available. T-Mobile was the only operator in the US supporting NB-IoT prior to Verizon and AT&T getting into the game.
Cellular offers many advantages over Wifi and other technologies. Mainly, security and automatic activation. Dealing with activation on a Wifi network is cumbersome and Wifi is more easily hacked.
So depending on your applications needs, CATM and/or NB-IoT are two technologies that should be considered.