By Paritosh Bansal and Soyoung Kim

(Reuters) - SoftBank Corp is in talks with Deutsche Telekom AG over a possible deal for T-Mobile US Inc , as the Japanese company looks for alternatives to enter the U.S. wireless market if its $20.1 billion deal with Sprint Nextel Corp falls apart, according to three sources familiar with the situation on Friday.

SoftBank and Deutsche Telekom were in talks last year about a deal for T-Mobile USA and have had periodic discussions since then, but those conversations have intensified in recent weeks after Dish Network Corp made a $25.5 billion counterbid for Sprint, two of the sources said.

Deutsche Telekom owns 74 percent of T-Mobile US, and one possibility is for SoftBank to buy that stake if the Sprint deal doesn't happen, the sources said. T-Mobile US has a market value of about $15 billion.

T-Mobile's shares rose more than 3 percent after the news of Softbank's interest, while Sprint shares were off 0.5 percent.

SoftBank and Sprint declined to comment. T-Mobile did not have immediate comment. Deutsche Telekom did not immediately respond to a request for comment.

The news of SoftBank's talks comes ahead of a June 12 vote for Sprint shareholders to approve the Japanese company's bid for the No. 3 U.S. wireless carrier and could add pressure on investors as they decide how to vote.

The SoftBank deal is much farther along in the process than Dish's rival offer. Softbank has cleared a key review by the agency that oversees foreign investments in the United States and is also getting closer to finishing the Federal Communications Commission review.

SoftBank still wants to do the Sprint deal after spending months on it, and is looking at a possible T-Mobile transaction only as "Plan B", the sources said who declined to be named because the talks are private.

If SoftBank decides to walk away from the Sprint deal, it would stand to make somewhere around $5 billion from currency hedging gains, its previous purchase of Sprint shares and breakup fees, the sources said.

(Reporting By Paritosh Bansal and Soyoung Kim in New York; Editing by Bernard Orr)