The number of pre-ordered Galaxy S8 and S8 Plus handsets to start being used has dropped drastically two days after official services began.
Only 63,400 of the phones started services on Wednesday, one third of the previous day's 210,900.
Telco sources told ZDNet that the popular Galaxy S8 Plus that comes with 6GB RAM and 128GB internal memory was facing supply issues.
Samsung has previously said the popular model will be arriving late for some.
Samsung said a total of 1.004 million Korean pre-orders came in by the time the pre-order window closed on Monday. It began shipping the phones on Tuesday.
The company had targeted 1 million pre-order Galaxy S8 sales in its home country, five times the figure Samsung achieved with the Galaxy S7 and S7 Edge last year.
The million pre-order figure is an all time record for a smartphone in South Korea. Around a third of the Korean pre-ordered units have gone online before official sales start this Friday, April 21 -- also a record.
Samsung is conducting pre-order sales for the phones in US and Canada, as well as Korea. It began pre-orders in India on Thursday. Sales in China will likely begin sometime in May.
Some Korean consumers have received the new devices with red-tinted screens, which Samsung said can be fixed manually.