More than 130,000 KT customers have moved to other telecom carriers after KT introduced a waiver of early termination fees following an unauthorized small-payment incident.

Industry data on Wednesday showed that from Dec. 31, when the fee waiver began, through the previous day, the number of customers leaving KT totalled 130,599. Over the period, 74 percent of those who left KT chose SK Telecom.

On Jan. 7 alone, total number portability transactions reached 51,229, with 23,100 KT subscribers leaving. Of those, 23,100 switches were to SKT, 14,298 to LG Uplus and 3,917 to budget carriers known as MVNOs.

KT is stepping up efforts to retain departing customers. On Jan. 7 it released details of a "customer rewards programme". Starting next month, it will provide an additional 100 gigabytes of data for six months and allow customers to choose one of two OTT services, including TVING, for six months of free use. It will also offer publicly posted device subsidies of up to several hundred thousand won to subscribers on low-cost plans priced in the 30,000-won range per month.

By contrast, SKT operates a programme that restores membership tenure and membership grade for customers who rejoin after cancelling their SKT line between April 19 and July 14 last year.

Authorities have begun steps to prevent overheated competition. The Broadcasting Media and Communications Commission will intensively inspect cases in which sales outlets promote "free phones" and bundle various add-on services that result in additional costs, or offer terms that differ from online advertisements.