A review of AT&T’s wireless coverage map of the Triangle area shows its 4G LTE wireless service now blankets the region, and on Monday the telecommunications giant gave some insight into how that has come about.

The company says it has spent some $350 million in the Raleigh-Cary-Durham-Chapel Hill area over the past three years in upgrading wireless and landline networks.

That total makes up a pretty good chunk of the some $1.5 billion AT&T says it has spent across North Carolina over that same time frame.

Most of the money invested in the Triangle came in Raleigh-Cary at $250 million, AT&T said.

AT&T’s 4G LTE [long-term evolution] technology extends, which delivers data at broadband speeds, beyond the Triangle to the Triad, Charlotte, Wilmington and Fayetteville.

In some areas, older, slower 4G technology known as HPSA+ is still in use but will be augmented over time by LTE equipment, according to AT&T spokesperson Josh Gelinas.

“Rather than replace HSPA+, the LTE network will augment it,” he explained. “So, for example, if a customer lost connectivity to the LTE network, instead of falling back to a 3G network, they would access HSPA+, providing better service than 3G and preventing a jarring drop in data speeds.”

AT&T launched 4G LTE service in the Triangle in January of last year. The company says that customers suffered 1 percent dropped calls in the last quarter of the year.

“We know the mobile Internet has become central to our customers’ lives, and we’re committed to driving both investment and innovation to deliver the best possible experience over the AT&T network,” said Laurent Therivel, AT&T vice president general manager in the Carolinas. “While third-party and internal testing shows that these investments are paying off with excellent service for Raleigh area customers, we are continually planning and deploying network enhancements to improve service in the future.”

Just last month, AT&T also announced plans to acquire Alltel’s wireless business, which has a considerable presence across the state.

Investments statewide included adding or upgrading some 1,475 cell sites.