– Shares of T-Mobile US Inc., the fourth-largest U.S. wireless carrier, jumped the most in more than a year after the Wall Street Journal reported that rival Sprint Corp. is considering a bid for the company.

The shares rose 8.6 percent Friday to close at $27.64, marking their biggest one-day gain since October 2012. The stock has climbed 39 percent this year.

Sprint, the third-largest carrier, is studying antitrust concerns and could push ahead with a T-Mobile bid in the first half of next year, the Journal reported, citing unnamed people familiar with the matter. Such a deal would leave the U.S. with only three major mobile-phone services, potentially raising the hackles of regulators. AT&T Inc. abandoned a $39 billion bid for T-Mobile in 2011 after facing opposition from the Justice Department and the Federal Communications Commission.

"There is little chance for a Sprint/T-Mobile deal to get through regulators over the next two years," said Walt Piecyk, an analyst at BTIG in New York.

Sprint, based in Overland Park, Kan., hasn't decided if it will make a bid, the Journal said. The deal could be worth more than $20 billion, depending on how much of a stake Sprint buys, the newspaper reported. T-Mobile had a market valuation of $22.1 billion at the end of today's trading.

Janice Kapner, a spokeswoman for Bellevue, Wash.-based T-Mobile, declined to comment to Bloomberg News. Bill White, a spokesman for Sprint, didn't immediately respond to a request for comment.