The logo of U.S. mobile network operator Sprint Corp is seen at a Sprint store in San Marcos, California August 3, 2015. REUTERS/Mike Blake /File Photo

NEW YORK (Reuters) - Sprint Corp is offering free unlimited data, talk and text for a year in an aggressive promotion launched on Tuesday, aimed at Verizon customers in an oversaturated U.S. wireless market.

Customers who switch to Sprint before June 30 and bring their own devices will get free service until July 31, 2018, the No. 4 U.S. wireless carrier said. After that, Sprint’s regular rates for unlimited plans will kick in, at $60 per month for a single line.

The promotion mainly targets Verizon Communications Inc customers through digital advertising, Sprint spokesman David Tovar said by phone.

Sprint shares rose 0.6 percent to close at $8.26. Verizon fell 1.5 percent, and both T-Mobile US Inc and AT&T Inc lost about 1 percent.

The S&P 500 Telecommunications Services Index was the weakest of the benchmark S&P Index’s 11 sectors after the launch, with a 1 percent decline mostly driven by Verizon and AT&T.

Since the offer will be promoted digitally rather than on television, the cost of winning customers is lower than for Sprint’s other unlimited plan promotions.

Craig Moffett, an analyst at MoffettNathanson, in a research note on Tuesday called the offer “arguably the most aggressive promotion in the history of the U.S. wireless industry.”

All four major U.S. wireless carriers have been sweetening their unlimited plan offers, prompting concerns from industry analysts about an accelerating price war.

But Roger Entner, an analyst at Recon Analytics, said the promotion “makes a really big splash in a really small pool,” noting that it primarily applied to Verizon users because of the phones that are eligible.