OFCOM, the British regulator, reports mobile data use per subscriber increasing 25% in 2018. Telefonica Deutschland expects the growth rate from 2017 to 2020 to be 37%, presumably higher in the earlier years. Cisco's VNI predicts North American wireless growth of 31% in 2022. The traffic growth rate is crucial to get accurate; it determines when a company needs to invest to avoid a problem.
In the chart at left from Cisco VNI data, the blue is 2018 growth and the red the projection for 2022. Every region falls. That corresponds to the experience of almost every country. Growth is rapid when smartphones are being adopted then falls off when most people have smartphones. In Australia, traffic spiked when Netflix arrived. Netflix is now in most countries, so that will be rare going forward.
The important exception is China. Government and company figures are growth over 80% in 2018 despite wide smartphone ownership. My guess is that the increase is due to increased TV watching, as video on demand services like Tencent Video, Youku, and iQIYI have grown very rapidly. Cable TV subscriptions have fallen the last two years at one of the highest rates in the world.
One possible contradiction is the 80% growth in U.S. wireless in 2018 reported by the CTIA trade association. This is almost certainly an artefact. 90% of U.S. wireless is four companies, which individually have reported much lower rates. In 2017, CTIA reported only 20% growth when the companies reported 35% to 50%. The two-year average growth was a much more reasonable 40%-45%. It could be explained, perhaps, if one of the large carriers reported its data late and it was pushed from 2017 to 2018.