Softbank acquired eAccess in a $1.84bn deal.
Softbank has made eAccess a wholly own subsidary this month.
The company signed a contract to acquire mobile carrier, Sprint Nextel,and is finalising negotiations to sell nearly 67% of its stake in eAccess to Samsung and 10 other firms.
The sale, which is in line with Japan's Internal Affairs and Communications Ministry's regulations on allocating frequency bands to mobile phone carriers, is expected to allow Softbank to hold a monopoly on spectrum allocation designated by the Communications Ministry.
The Nikkei business newspaper reported that either a parent firm, or one of its units in which it owns more than 33% will be allowed to apply for an allocation of spectrum.
Other companies involved in acquiring the stake include LM Ericsson, Nokia Siemens Networks, Orix and five Japanese leasing firms.
The company has opted not to allow any Chinese firm to acquire eAccess shares in a bid to avoid any impact on its operations in the US.
Most of the shares in eAccess, which will be retained by Softbank, will not have voting rights.