The interjection 喂
An interjection (感叹词) is a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling or reaction. It expresses feelings and emotions but does not name them. It is usually placed at the beginning of a sentence.
喂 has two different meanings based on the intonation:
1) 喂 
is used when answering the phone and translated as “hello”.
is used when answering the phone and translated as “hello”.Examples
喂，是谁？
Hello, who’s this?
wéi, shì shéi
喂，是王经理吗？
Hello, is this director Wang?
wéi, shì wáng jīnglǐ ma
2) 喂 is translated as “hey” in informal speech.
is translated as “hey” in informal speech.Examples
喂，那里有人吗？
Hey, is anybody here?
wèi, nàli yǒu rén ma
喂，镇静一点！
Hey, calm down!
wèi, lěngjìng yìdiǎn
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