In the United States, smartphones have even begun reaching the group of relative technophobes that consumer researchers call the “late majority.” About half of mobile-phone users now have one.

The big question facing technology companies, and the subject of the upcoming stories in this month’s MIT Technology Review Business Report, is how to make money from this rapidly expanding technology.

Wireless carriers make money at the greatest scale. Globally, 900 of them take in $1.3 trillion in revenue each year, about four times the combined revenue of Google, Apple, Microsoft, and Intel. Yet individual device makers, notably Apple, capture more profit. That company’s markets aren’t restricted to one network.