In the battle of billionaires trying to enter the U.S. wireless market, Dish Network Corp.'s Charlie Ergen has won a round against SoftBank Corp.'s Masayoshi Son.

Clearwire Corp.'s board endorsed Dish's $4.40-a-share bid for the company this week, spurning an offer by its majority owner, Sprint Nextel Corp. The move deals a setback to Tokyo-based SoftBank, which sees a Sprint-Clearwire combination as the centerpiece of its U.S. expansion plan. SoftBank is vying with Dish to acquire Sprint, the third-largest U.S. wireless carrier.

Sprint separately agreed this week to a $21.6 billion takeover by SoftBank, rejecting a higher offer by Dish that it said was not "actionable." If Dish is able to acquire the portion of Clearwire that Sprint doesn't own, it could force the carrier to reconsider whether SoftBank is its best suitor, said Walt Piecyk, an analyst at BTIG LLC. Without full control of Clearwire and its valuable airwaves, Sprint won't be able to execute on its plans for a fourth-generation network, he said.