I think it's intentional. I use Google Voice as my primary phone number, and there are various services that won't let me use it for 2FA, etc. I opened a support ticket with Discord to ask why, and after many emails back in forth they told me they have a database of what type of phone number every phone number is, and mine is "VoIP" which they claim cannot receive SMSes. (Everyone else, including my bank, has no trouble, of course... because they check by sending the SMS, not asking some outdated database if it's possible to send the SMS.)
What they didn't tell me, but I assume, is that some popular discord servers require phone verification to limit spam... and if anyone could just use a VoIP number as that phone verification, then that wouldn't work. (It still doesn't work, of course, but they think it does.) I, of course, just want to have an account recovery phone number, but they conflate the two uses of the phone number (person identifier, versus arbitrary second factor).
TL;DR, a lot of places are dumb and intentionally prevent you from using any sort of "recyclable" phone number. It helps them keep up the illusion that a phone number uniquely identifies exactly one person. Maybe that's true in South Korea, but it isn't here. So it just screws legitimate users for no reason.
What they didn't tell me, but I assume, is that some popular discord servers require phone verification to limit spam... and if anyone could just use a VoIP number as that phone verification, then that wouldn't work. (It still doesn't work, of course, but they think it does.) I, of course, just want to have an account recovery phone number, but they conflate the two uses of the phone number (person identifier, versus arbitrary second factor).
TL;DR, a lot of places are dumb and intentionally prevent you from using any sort of "recyclable" phone number. It helps them keep up the illusion that a phone number uniquely identifies exactly one person. Maybe that's true in South Korea, but it isn't here. So it just screws legitimate users for no reason.