The Internet conglomerate that owns Japan's third-largest as well as major online properties such as Yahoo Japan and large investments in foreign companies such as China's Alibaba Group, has aggressively expanded under the leadership of its CEO and founder Masayoshi Son.

Son has repeatedly made large gambles to expand his holdings in the past, including entering Japan's closed fixed-line Internet business, the acquisition of Vodafone's Japanese subsidiary, and betting big on Apple's first iPhone.

Combining Softbank and Sprint could make it cheaper for the new entity to purchase network equipment as well as phones and tablets for its network. Softbank's potential investments in the U.S. could also pass the scrutiny of domestic regulators, as it wouldn't reduce the number of operators in the country.