Around 30,000 KT subscribers switched to other carriers or budget mobile operators over three days after KT introduced a penalty fee waiver, data showed.

Industry data on Friday showed the total number of subscribers who left KT from Dec. 31 to the previous day was 31,634. That is more than 10,000 a day on average. Most, 26,192, chose other carriers rather than budget operators.

Of those, 18,720 moved to SK Telecom, accounting for more than 70 percent. The number who switched to LG Uplus was 7,272.

By day, 7,664 moved to other carriers on the first day the waiver began. Of those, 5,784 switched to SKT. Over the next 2 days, 18,528 moved to rivals, including 12,936 who switched to SKT.

Industry players cite the impact of SKT's subscriber acquisition policies as a reason KT leavers are concentrating on SKT.

SKT has been restoring subscription tenure and membership grades for rejoining customers since last year's hacking incident, and some analysis says customers who had left are returning as KT's penalty fee waiver takes effect.

Industry players cite perceived benefits of KT's customer compensation package as a factor behind customers leaving. KT has announced measures linked to the hacking incident, including waiving early termination fees, providing extra data and expanding membership benefits. But the biggest benefit, extra data, does not go to users of unlimited data plans, who make up about 30 percent of subscribers.