The overall increase for the month amounted to a rise of 0.3 percent to 38.06 million users, or 78.86 percent of the country's population.
Second-ranked KTF Co Ltd gained a net 28,820 customers to bring its tally to 12.3 million users, controlling a 32.34 percent stake of the market, versus a 32.4 percent share a month earlier.
Shares in SK Telecom closed up 0.3 percent at 188,000 won, versus a 2.7 percent rise in the broader market.
Shares in KTF finished up 0.7 percent and LG Telecom closed up 3.7 percent.