It’s your move, Charlie Ergen.

After SoftBank Corp. raised its offer for Sprint Nextel Corp. to $21.6 billion last night, the spotlight returns to Ergen, the Dish Network Corp. chairman who made an unsuccessful $25.5 billion counterbid in April.

In endorsing SoftBank’s new bid, Sprint said yesterday that Dish never made an “actionable” counterproposal. After talks broke down, Sprint asked Dish to destroy the confidential information it supplied to the company. The onus is on Ergen, a billionaire and one-time professional blackjack player, to produce a more compelling offer, said Sprint investor Leon Cooperman, head of Omega Advisors Inc. in New York.

“Let’s see how Mr. Ergen responds,” said Cooperman, whose firm held 65.2 million Sprint shares as of March 31.

SoftBank, the Japanese mobile-phone carrier controlled by Masayoshi Son, is now offering to pay $16.6 billion to Sprint shareholders, plus an injection of $5 billion in new capital, in return for a 78 percent stake in the U.S. company. If it wants to counter, Dish has until June 18 to make its “best and final” proposal, Sprint said.

SoftBank -- which has the backing of Sprint’s board and its second-largest investor, Paulson & Co. -- plans to use the carrier to expand into North America. Ergen, meanwhile, wants to add Sprint’s wireless services to his company’s satellite-TV offerings.

SoftBank’s Terms

SoftBank plans to acquire shares from existing Sprint investors for $7.65 apiece, up from the previous offer of $7.30, the company said in its statement. The initial SoftBank bid for Overland Park, Kansas-based Sprint in October was $20.1 billion for a 70 percent stake.

Sprint’s stock rose 2.5 percent to $7.36 at 9:38 a.m. in New York. Shares of SoftBank fell 0.4 percent to 5,500 yen at the close of trading in Tokyo.

“I am withholding judgment until Ergen responds,” said Sprint investor Roy Behren, who co-manages the $4.7 billion Merger Fund at Westchester Capital in Valhalla, New York. “The party may not be over yet.”

A Sprint shareholder vote on the SoftBank proposal was postponed to June 25 from June 12. The breakup fee for the deal also increased to $800 million from $600 million. The companies expect their transaction to close in early July.

Dish Bid

Dish’s April offer included $4.76 cash and 0.05953 Dish shares for each Sprint share. The bid was worth $7 a share, and Sprint investors would own 32 percent of the combined company, Dish said at the time.

Sprint said yesterday that the Dish bid was “not reasonably likely to lead to a superior offer.” Dish responded last night that it was considering its strategic options.

“We will analyze the revised SoftBank bid,” Englewood, Colorado-based Dish said in a statement. “We continue to believe that Sprint has tremendous value.”

SoftBank has argued that Dish’s offer would burden Sprint with too much debt. SoftBank also is a better fit for Sprint, Paulson & Co. said.

“In addition to the improved financial terms, Paulson believes SoftBank has exceptional operating expertise in the wireless area and a strategic vision,” the investment firm said in a statement. Paulson owns 231 million Sprint shares.

ISS Backing

Institutional Shareholder Services Inc., the biggest shareholder-advisory firm, recommended SoftBank’s earlier bid in a report this month, saying the deal would supply Sprint with the cash it needs to upgrade its network and compete with larger carriers.

“The amended agreement announced today delivers more upfront cash to Sprint stockholders, while still achieving our goal of creating a well-capitalized Sprint,” Son said in yesterday’s statement.

Sprint’s board initially approved the SoftBank takeover in October after months of friendly discussions with the Japanese carrier. Sprint and SoftBank have received national-security approval for the deal from the U.S. government.

Dish and Sprint also are competing for Clearwire Corp., a wireless-network operator that is about 50 percent owned by Sprint. Sprint, which has been attempting to buy the rest of Clearwire since December, has faced two Dish counteroffers for the stake. Dish’s current bid values the wireless broadband provider at $6.5 billion.

The bidding war for Sprint has set up a battle of billionaires vying to expand into new territory. Son is the 66th richest person in the world, with a net worth of $13.6 billion, according to the Bloomberg Billionaires Index. Ergen is ranked 87th, with a net worth of $11.8 billion.

“You can’t rule out the possibility that Dish will raise its offer and SoftBank will again counter it,” said Hiroshi Yamashina, an analyst at BNP Paribas SA in Tokyo. “It’s hard to say this will be final.”

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