~500M Africans, Indonesians, and Indians are regular Internet users without a landline. Brazil, Indonesia, and Mexico add ~200M more. In total, something like 1B people were wireless-only at the end of Q3 2017. I'm comparing the number of Facebook users (over 250M in India) with the number of landlines (< 20M in India) for a rough guess at how many are wireless only. In the developed world, 70-90% of all homes have a landline connection, implying fewer than 100M are wireless only.
About 65% of Internet users are now in the Global South. The gap is increasing by about 50M/year.