The use of 拜拜 over 再见 at the end of a phone conversation is obvious as you haven't seen them so how could you see them again but I don't understand why 喂 is used as a greeting when answering the phone.
It also seems the other dialect in Chinese use a different greeting for phone calls as compared to face to face interaction eg. Cantonese 喂 wái | Hakka 噯 oi
So my question is why was a different greeting needed for answering the phone?
Most languages use an alternate greeting for telephone calls; the English "hello", although originating from before the telephone, was popularised by it, so much so that it has become a common greeting outside the telephone:
1883, alt. of hallo (1840), itself an alt. of holla, hollo, a shout to attract attention, first recorded 1588. Perhaps from holla! "stop, cease." Popularity as a greeting coincides with use of the telephone, where it won out over Alexander Graham Bell's suggestion, ahoy. Central telephone exchange operators were known as hello-girls (1889).
So the mandarin 喂 is not an exception, only that unlike "hello", people do not use it outside telephone calls.
The reason for telephone greetings is that it was a medium where reception may be bad and you are unsure who you are talking to. Thus a short greeting meant to solicit response (i.e. "can you hear me") is used.
喂 is not only used in phone call, it was even used before the invention of phone. If you have watched lots of Chinese movies you may find that before people yell to another guy in mountain across a valley, yell through a tunnel, a pipe or even a well also start with 喂, the word 喂 is usually used as attracting attention and building connection.
After we can use a phone to talk to a people far away, we also consider this thing is similar to a pipe, tunnel or talk between two mountains, we need to build connection first, so we say 喂 to attract attention. Today, phones are very popular and people are used to start with 喂, using other words as greeting for phone calls make people uncomfortable instead.
再见 should not be translated as "see you again", the meaning of 再见 is just good bye, many Chinese words' meanings are not just the combination of the meanings of the two characters, you should be careful with that in your further learning.
“ 喂” actually is not a greeting word, when telephone just appeared in China, its signal was not very stable( I think it’s the same in other countries), so when people was calling somebody, they first need to make sure the person on the other end of the phone could hear their voice, so they used “喂” , “喂” is just a word people using to make some sound to test their partner can hear them. We actually after say “喂”， we will greet people again, like” 喂？ 你好.” Actually when you want to call somebody you don’t know on street, you can also say “ 喂”（but use the fourth tone this time ）. Or in KTV when we want to test the microphone is good or not, we will also say “喂，喂……”.
There is also the question of formality. "喂，你好" is a pretty common way of answering the phone, too... It just depends on who you are talking to. 你好 is way more formal than most foreigners realise. You'd never use it with your friends (unless there is a large age gap)... That would just sound weird.
Saying 喂 is like saying "Hi..." when you answer a phone in Chinese. The following are some common phrases that can used to answer a phone. 喂，你好。 wéi, nǐ hǎo. Hello. 小王在吗? xiǎo wánɡ zài mɑ? Can I speak to Xiao Wang? 对不起，你打错了。 duì bù qǐ, nǐ dǎ cuò le. Sorry, you made a wrong call.
And this is a good place to know more simple Chinese phrases in different life situations.
auf wiedersehenthey sayauf hörensehenover the phone...