It still seems crazy that even though carriers knew how easy it is to spoof numbers, even back then, they still decided to just skip any voicemail passcode auth

It still seems crazy that even though carriers knew how easy it is to spoof numbers, even back then, they still decided to just skip any voicemail passcode authentication if you were calling your own number from your own number to get to your voicemail. It's like letting someone in your house because they're holding up a paper cutout of someone else's face that you know in front of their actual face and that's good enough.