Former state-owned monopoly KT was given the stamp of approval at a Korean Baseball Organisation (KBO) general meeting, where owners of the league's other nine teams gave it the edge over conglomerate Booyoung Group.
The new team will have its home base in Suwon, south of Seoul, and play in the second tier in 2014 before becoming the top flight's 10th professional ballclub a year later.
KT CEO Lee Suk-chae said the league expansion was a milestone for Korean baseball.
"I deeply appreciate the KBO's decision to select KT and Suwon City as the 10th member to begin a new history of Korea's pro-baseball league," he said in a statement.
"I want to thank all of the other teams that are trying their best for the development of the Korean baseball league.
"We would like to share this joy with all of Suwon and Gyeonggi Province residents and KT employees."
Lee also paid tribute to rival Booyoung, who had been looking to take professional baseball to Jeonju, the capital of southwestern province North Jeolla.
"I would like to express my sincere gratitude to Booyoung and North Jeolla province for the competition in good faith," he added. "Had it not been for the friendly rivalry with them, we would never have come up with ways to improve the Korean baseball league."
South Korean baseball has enjoyed continuing growth in recent years and posted a record $33 million in revenue in 2012.
Winning gold at the Beijing Olympics and finishing runners-up at the 2009 World Baseball Classic boosted baseball's popularity and attendances crossed the 7 million-mark for the first time last year.
The league pocketed 35 billion won ($32.9 million) in 2012, bettering the 34 billion it earned a year earlier, a recent media report said citing figures from the marketing wing of the KBO.
Yonhap News agency reported KT would have to pay 3 billion won ($2.8 million) as a league entry fee and stump up 20 billion for the KBO's development fund.
The company would also have to put up a security deposit of 10 billion won to guard against the team running into financial difficulties or if KT fails to provide a new stadium with at least 25,000 seats for the team.
($1 = 1058.7500 Korean won) (Reporting by Narae Kim in Seoul, Writing by Peter Rutherford in Singapore; Editing by Amlan Chakraborty)