So I actually went looking for this a few weeks back because I much prefer listening to webnovels during my commute. 'The Number You Have Dialed' is one of those stories that seems to have a huge online following in its original text form, but when it comes to official audiobook adaptations, it's a bit of a dead end right now. I searched major Korean audiobook platforms like Audible Korea, Millie's, and Ridibooks, and came up empty. It doesn't seem to have gotten the professional narration treatment yet, which is a shame because the tense, dialogue-heavy premise would lend itself really well to audio.
What you will find, though, are a ton of user-generated readings on YouTube and some podcast apps. These are fans recording chapters themselves. Quality varies wildly—some are basically just monotonous reading into a phone mic, while others have decent production with sound effects and attempts at vocal characterizations. It's a bit of a treasure hunt, and you have to be okay with incomplete series since these projects often get abandoned. If you're desperate to experience it in audio and don't mind the unofficial route, that's your only current option. I listened to a few chapters of one such reading; the voice for the male lead was trying way too hard to be gravelly and intense, which honestly made some scenes unintentionally funny.
Given the story's popularity, I wouldn't be surprised if a platform picks it up for a proper adaptation eventually, but for now, it's text-only on the official sites. I ended up just reading it on my phone.