San Francisco

EVERY few years, mobile carriers promise to turbocharge smartphones with new "G" technology. Most recently, 4G began replacing 3G, and people from Trenton to Tacoma celebrated the fact that they could watch cat videos without their screens locking up (well, most of the time).

This summer, Verizon Communications Inc and AT&T will start testing 5G. If this fifth-generation mobile network works as advertised, it could be far more transformational than previous versions, accelerating adoption of the Internet of Things: smart homes, driverless cars, surgical robots and more. According to one estimate, the number of connected "things" could more than double to 50 billion globally by 2020 - and reach 500 billion 10 years after that.