Workplace-software providers Ultimate Software and Kronos Inc. plan to merge, according to people familiar with the matter.

The all-stock deal would create a company worth roughly $22 billion including debt, the people said. Hellman & Friedman, the private-equity firm that controls both companies, would remain the controlling shareholder, while Blackstone Group Inc., which owns stakes in both, would be the largest minority investor in the combined company.

A decision by U.S. District Judge Victor Marrero, after a December trial, would clear the way for the $26 billion merger of the No. 3 and No. 4 wireless carriers by subscribers. The companies agreed to merge nearly two years ago. They secured approval from federal antitrust and telecommunications officials last year after T-Mobile and Sprint made concessions.

In after-hours trading, Sprint shares surged 53% to $7.37 following The Wall Street Journal report, while T-Mobile added 8% to $91.60.

—Sarah Krouse and Brent Kendall contributed to this article.

Write to Cara Lombardo at cara.lombardo@wsj.com and Drew FitzGerald at andrew.fitzgerald@wsj.com

Elliott Management Corp. has quietly built up a more than $2.5 billion stake in Japan’s SoftBank Group Corp. and is pushing the sprawling technology giant to make changes that would boost its share price, according to people familiar with the matter.

Founded by billionaire Paul Singer, New York-based Elliott is known as a formidable activist investor, often seeking to influence company management. SoftBank is one of Elliott’s largest bets, according to people familiar with the matter. At current prices, the investment would...

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