In 2013, KPN was the first to roll out the LTE (3.9G, but popularly called 4G) network. LTE is designed to be backwards compatible with the older (3G and 2G) systems. This allows antenna systems and other equipment to be used in combination.
LTE is much more flexible when it comes to bandwidth allocation, which means there is less congestion. There are several categories of LTE, but only a few are suitable (in terms of chip price and power consumption) to be used is in IoT or telemetry devices.