WESTBROOK — As part of a campaign to build public support for its proposed merger with T-Mobile USA, AT&T on Monday outlined the progress it has made this year upgrading its wireless network in Maine.

The communications giant has expanded mobile broadband in 26 communities from York County to Washington County, as well as wireless network capacity in 60 communities. From 2008 through 2010, the company spent nearly $60 million on wireless and landline networks in Maine.

The investments support efforts to bring wider coverage and faster, so-called 4G service to customers at a time when exploding demand for wireless Internet access is being driven by smartphones, tablets and laptops. AT&T already offers last-generation 3G service to about 75 percent of Maine’s population, according to company estimates.

AT&T officials outlined their 2011 plans after a media tour of a switching facility that handles an average of 6.5 million wireless calls per day in Maine and New Hampshire. The facility’s recent upgrade to handle 4G speeds reflects AT&T’s commitment to Maine, said Owen Smith, the company’s regional vice president for the state.

On a national level, the company has invested $19 billion in the past three years, he said, adding, “We will continue to invest that kind of money.”

In an interview with The Portland Press Herald, however, Smith noted that much of the capacity has been added around urban areas. Acquiring T-Mobile’s tower sites and airwave spectrum is important to AT&T’s expansion schedule in rural Maine, he said.

“Without T-Mobile, that will be delayed,” he said.

Smith’s position was echoed by Steve Krom, the company’s vice president and general manager in New England. He called the merger “critical” and said he is confident that it will be approved by the Federal Communications Commission.

One asset that AT&T would get in the merger is a 6-year-old call center in Oakland that’s operated by T-Mobile. The $17 million center has 700 workers and is a major employer in the Waterville area.

When the merger was first announced, U.S. Sens. Olympia Snowe and Susan Collins, R-Maine, contacted AT&T to voice concern about the future of the call center. At Monday’s event, Smith said the facility would remain open after a merger.

“AT&T has no plans to close that,” he said.

In March, AT&T announced plans to buy German-owned T-Mobile for $39 billion. The merger would be the quickest and most efficient way to gain network spectrum and capacity, the company said. It would benefit customers by improving and expanding service, and making new technologies more available.

Critics say the deal would be bad for consumers.

Approval would give AT&T and Verizon control over more than 80 percent of the U.S. market, they say, creating a “duopoly” that would stunt competition. It would restore a degree of domination that the government sought to break up when the old Bell telephone system was dismantled in 1984 and the country’s telecom market was deregulated in 1996.

Such concerns have led Sprint, the sole remaining national carrier, to oppose the merger. Two states, California and Louisiana, are looking into the sale’s effect, and other states may follow.

In Maine, the Public Advocate’s Office is likely to join with its national association of utility and consumer advocates to file comments with the FCC, said Wayne Jortner, a lawyer with the Maine office.

“Less choice for consumers tends to lead to higher prices,” he said.

The media tour of the switching center, Jortner said, was merely “a smoke screen” for the AT&T merger campaign.

“They’re just trying to promote the merger,” he said. “They don’t have to get bigger to invest in Maine. They’re already huge.”

AT&T’s expansion in rural Maine would put it into more direct competition with a regional carrier that has gained a strong presence in the state, U.S. Cellular. The company is putting up 30 new towers this year and is preparing to roll out 4G service in selected Maine communities.

“We don’t expect it to impact the way we do business. It makes us even more confident in our strategy to differentiate U.S. Cellular through the ideal customer experience we deliver,” said Eric Conlon, director of sales in New England, in a prepared statement.