Just kill the phone. It's a terrible anachronism. If you insist on voice you can attach an ogg/mp3 file to your email.
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Legitimacy aside, the only people who still call me without prior arrangement tend to be those who assume they’re entitled to my time and attention on demand. The phone has always been a disruptive form of communication—even if every single call were legitimate (which is far from reality)—because it disregards the boundaries of the recipient’s time.
That’s why I stopped giving anyone real-time PSTN access. For me, it’s voicemail-only now, and honestly, it’s the best decision I’ve made for cutting down on annoyances.