What is the etymology and glyph origin of 餵? I was surprised to find out about the character 餵 (wei4, 喂) because it doesn't seem to have a meaning other than an expression to answer the telephone. Since the telephone was only invented in the last hundred years or so...this must be a relatively new character. Is this accurate? If so, how was the character/sound developed?
喂 means feed(verb) originally besides answering telephone. 

Regarding the origin of the character, according to CiYang

(1) (餵、喂是近代的“餧”字) 喂食    餵 and 喂 are modern writing of 餧
餧,饲也。——《玉篇》    餧 means feed(verb)


It's a new character derive from 餧.

P.S. The most popular usage of 喂 may be a character for answering phone. But it is also a derivative from the common usage of saying hello in a rude way.  Because of this, in fact, there are many people claims that answering phone with 喂 is impolite, we'd better say 你好/您好 instead. If you call public service number like customer service hot lines, you always hear the operator answering 您好.