Mobile phone companies advertise high-speed 5G service with US maps splashed with pink or blue to suggest widespread coverage, but the latest generation wireless technology is actually only available less than a third of the time in the best-served states, new data shows.

5G technology was designed to be faster than 4G wireless, with so little latency to help make things like driverless cars possible. 5G running on low band spectrum is the slowest, but it has the advantage of considerable range while mid-band can't travel as far, but is faster. The high band spectrum, which is sparsely available, may travel only a mile but is by far the fastest...