After the "will they or won't they" mess of negotiations between Deutsche Telekom, the reluctant owner of T-Mobile US, and SoftBank Corp., the owner of Sprint fell apart once again, SoftBank has announced their intent to increase their ownership stake in Sprint. This change would increase SoftBank's control of the US's 4th largest mobile network operator from 80% to 85%.
The 2017 series of negotiations centered around SoftBank selling their stake in Sprint to Deutsche Telekom, which were apparently abandoned on November 5th due to concerns from members of SoftBank's board about ceding control of the company. This is a reversal of the 2013-2014 series of negotiations, in which SoftBank sought to acquire T-Mobile US. That plan was abandoned under the expectation that it would not clear regulatory hurdles.
T-Mobile US was also an acquisition target by Iliad SA, the operators of the French telecom Free Mobile in 2014, and by AT&T in 2011. Additional rumors indicated Deutsche Telekom was in negotiations with Comcast to sell T-Mobile US in 2015.
SoftBank's acqusition of Sprint in 2012 was modeled after the company's previous success acquiring and rehabilitating Vodafone Japan, which was hemorrhaging subscribers when it was acquired in 2006. SoftBank later acquired Japanese mobile operator Willcom while it was going through bankruptcy proceedings. Much like the proposed Sprint / T-Mobile merger, the acquisition of Willcom blended two fundamentally different network architectures into one company.