In a recent interview, a FirstNet spokesperson characterized potential reconstitution costs incurred by states opting out and failing to create networks, then needing to join FirstNet as "estimates of the very worst-case numbers", and said FirstNet has worked closely with all states and territories to help them make the most informed decisions of whether to opt in or out.

The release mentioned "first responder subscribers", but did not specifically say how the network will be paid for. In addition to the states, Washington, D.C., Puerto Rico and the U.S. Virgin Islands also opted for FirstNet, AT&T said. "Because New Hampshire started early and conducted a thorough evaluation of both paths, we were presented with a strong opt-out plan that strengthened the state's negotiating position".

The governor said the decision means that AT&T will build 48 new cell tower sites across the state.

Wall Street analysts have said FirstNet is a way for AT&T to add to its portfolio of wireless airwaves, or spectrum, at a time when consumers are using more data on their cell phones.

Sununu said opting out and going with Rivada would have given the state better coverage, more system control and an opportunity to share in revenue streams. All are participating, and American Samoa, Guam, and Northern Marianas Islands get until March 12, 2018 to decide.

"As a result, it now appears likely that no other states will opt out", Sununu said.

FirstNet is meant to provide a broadband system for first responders that can be used across state lines in the event of a major emergency. "Brown puts reliable communications and cutting-edge technology in the hands of California's first responders", FirstNet CEO Mike Poth said in a prepared statement. "FirstNet looks forward to our continued partnership with the state's public-safety community".

All but one of the nation's 50 states, along with two territories and Washington, D.C., have made a decision to join FirstNet, the dedicated, nationwide first responder network, by its December 28 deadline.

The opt-out decision, and the entire process leading up to a decision allowed the state to maintain leverage to "ensure that the AT&T proposal was one of the best in the country", Sununu said.