Tokyo - SoftBank has declined to comment about reports that it is in talks with DeutscheTelekom over a possible deal for T-Mobile US.
The Japanese company is looks for alternatives to enter the US wireless market if its $20.1bn deal with Sprint Nextel falls apart, sources say.
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 $25.5bn counterbid for Sprint.
Deutsche Telekom owns 74% of T-Mobile US and one possibility is for SoftBank to buy that stake if the Sprint deal doesn't happen, the sources say.
T-Mobile US has a market value of about $15bn.
T-Mobile's shares rose more than 3% after the news of Softbank's interest, while Sprint shares were off 0.5%.
Sprint, T-Mobile and Deutsche Telekom have not yet commented.
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 US 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.
If SoftBank decides to walk away from the Sprint deal, it would stand to make somewhere around $5bn from currency hedging gains, its previous purchase of Sprint shares and breakup fees, the sources said.
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