Samsung began the voice command service at 1pm KST on Monday, after sending a notice in the morning to users of the smartphones.
Bixby, the company's artificial intelligence (AI) assistant rolled out on April 21 when official sales of the Samsung Galaxy S8 and S8+ series began in South Korea.
Bixby supported vision, reminder, and home features but the voice command feature was absent. Samsung previously said it wanted to fully prepare before rolling out Bixby Voice Assistant.
Voice command is yet to reach other markets outside of South Korea where the Samsung Galaxy S8 and S8+ is available. US customers are rumored to get Samsung's Bixby Voice Assistant in May.