Sprint filed a proxy document with SEC, on behalf of SoftBank, which emphasises strong business links between the Japanese firm and US companies as part of its bid for Sprint.

The SEC filing lists a string of US companies that SoftBank has invested in, including Yahoo!, E*Trade, GSI Commerce, Huffington Post, Buddy Media, Ziff Davis, Gilt Groupe and Zynga.

SoftBank adds it has helped US media and technology companies – such as Yahoo!, Cisco and Microsoft – with access to growth opportunities in Japan.

For good measure, SoftBank says its $20 billion investment in Sprint “will have an enormous positive effect on the US economy”, creating job opportunities for US workers

SoftBank has faced opposition to its Sprint bid on patriotic grounds from Charlie Ergen, Dish chairman, who has tabled a counter-proposal for Sprint. The SEC filing is clearly designed to address those concerns.

Moreover, while Ergen has argued it would better if an American company took over Sprint, SoftBank implies in the SEC filing that its strong track record on running a mobile network in Japan will be far more beneficial for the US economy than choosing a homegrown firm with little mobile experience.

SoftBank further points out that foreign investment in the US telecoms sector is not new, citing the obvious examples of Verizon/Vodafone and T-Mobile USA/Deutsche Telekom.

For good measure, SoftBank says that if its bid for Sprint is successful, it will be joining “other respected Japanese companies”, such as Toyota and Sony, who have a strong presence in the US and have “contributed significantly to local economies”.

To placate any security concerns, SoftBank repeats its commitment in using only network equipment that’s acceptable to the US government, which effectively rules out Chinese suppliers Huawei and ZTE.

According to a Wall Street Journal report, SoftBank says that it would appoint a “security director” to Sprint Nextel’s board if its takeover bid succeeds.

Tension has been mounting in recent weeeks between SoftBank and Dish as each try to woo Sprint shareholders of the merits of their respective bids. Masayoshi Son, SoftBank’s chairman, has disparaged Dish’s offer, calling it “incomplete and illusory”. He claims there are few synergies to be had between satellite and mobile.

And while the $25.5 billion Dish offer is higher than SoftBank’s – SoftBank struck a $20.1 billion takeover deal with Sprint management in October 2012 – Son claims that once its faster schedule and lower debt are taken into consideration, the SoftBank offer represents a 21 per cent premium to Dish’s counter proposal.

Sprint has set 12 June as a tentative date for a special meeting for shareholders to vote on the proposed SoftBank deal.