喂 is a mouth 口 calling out, with 畏 lending the sound. It started as a shout to get attention — 'hey!' — and when telephones arrived in China, the shout moved onto the line.
喂 is the first word of every Chinese phone call — answered with a rising wéi? that means 'hello, who's this?'. Face to face it's a blunter 'hey!'. Its second job is tender: 喂 also means to feed — 喂猫 (feed the cat), 喂孩子 (feed a child). One character covers both shouting into phones and spooning rice into toddlers; tone of voice does the rest.
A mouth 口 calling into the phone — WEI? Hello?
Phone-喂 rises (wéi?) like a question; street-喂 falls (wèi!) like a poke. Same character, two attitudes.