Sprint Corp.'s resumed talks about a potential merger with T-Mobile US Inc., being held at the same time as discussions with cable companies, shows the lengths billionaire Masayoshi Son is taking to build scale for a wireless carrier facing increasing competition in the U.S.

The two mobile operators restarted discussions after Sprint's exclusive negotiating period with Comcast Corp. and Charter Communications Inc. expired at the end of July, according to sources.

Son, who leads Sprint's largest shareholder, SoftBank Group Corp., is pursuing all options for industry consolidation as he continues to weigh a potential offer for Charter. SoftBank has been considering making a formal takeover bid for the cable company and combining it with Sprint, people familiar with the matter said earlier.