Often, you have to buy a global number separately that allows PSTN phones to call you. Where the number is from makes a difference for people calling you. Here is the same text in Chinese (Traditional):
常見的情況是必須購買不同的國際電話號碼，才能接到 PSTN 電話。對打電話給你的人而言，號碼來自哪裡確實有差別。