Sprint has beefed up its buyout offer for Clearwire and its valuable spectrum assets only days after filing a lawsuit against Dish Network for a rival bid it claimed was unlawful.

Meanwhile, Masayoshi Son, chief executive of Japan’s SoftBank, says he’s confident his takeover offer for Sprint will go through after Dish failed to raise its bid for the third-largest operator in the US. The SoftBank chief says he has ambitions to create the “world’s largest company”.

As with the bidding contest between Dish and SoftBank to take control of Sprint, the duel between the satellite TV broadcaster and Sprint to buy out Clearwire has been acrimonious.

Sprint, which already owns 50.2 per cent of Clearwire, was miffed when the US wholesaler backed a higher bid from Dish, so ditching its previous allegiance to the mobile operator. To try and win back Clearwire’s favour, Sprint is using both force and persuasion.

The force is a lawsuit against both Clearwire and Dish, claiming the terms of the Dish offer are illegal and that the US wholesaler had no authority to recommend it

The persuasion is dramatically upping its offer for the Clearwire equity it doesn’t own, from $3.40 per share to $5, which values the company in excess of $14 billion. It trump’s Dish’s offer of $4.40 per share – recommended by Clearwire last week – by around 14 per cent.

“We believe Clearwire shareholders will approve the $5 offer from Sprint regardless of any new overtures from Dish,” said Walter Piecyk, a BTIG analyst, quoted by Reuters.

In addition to the increased price per share, Sprint and Clearwire have amended their merger agreement. The change includes a break-up fee of $115 million if the latest deal fails.

By winning over some previous dissenters to its $3.40 per-share offer, Sprint says it now has support from shareholders holding 45 per cent of Clearwire’s minority shares, just short of the 50 per cent it needs to take over the company.

The outcome of Sprint’s revised offer for Clearwire will no doubt be watched closely by SoftBank’s Son. It’s hard to imagine he would relish a successful bid by Dish, whose chairman, Charlie Ergen, has campaigned aggresively against SoftBank, saying that Sprint, in the interets of US security and US jobs, should be controlled by an American company.

By failing to meet a 18 June deadline to improve its offer for Sprint, however, Ergen has all but assured the Japanese firm’s entry into the US mobile market.

Speaking at a SoftBank shareholders meeting on 21 June, reported by Dow Jones Newswires, an upbeat Son – assuming the Sprint deal goes through – said that “we will become the world’s biggest company – by all measures, whether by sales, profit, or market cap”.

Son added that SoftBank faces a smaller challenge of revamping Sprint than it did when it took over Vodafone’s struggling operations in Japan in 2006. He noted that Sprint has a large line-up of smartphones, high-speed networks, and an operating profit that has already bottomed out.

Son added that the scale and buying power of SoftBank and Sprint combined will generate cost savings of about $2 billion to $3 billion a year in the first three years after the deal is expected to close in July.

Sprint shareholders are scheduled to vote on SoftBank’s revised offer on 25 June.