According to Cameron Chapman, "E-mail was first developed in 1971 by Ray Tomlinson, who also made the decision to use the "@" symbol to separate the user name from the computer name."
Needless to say, this was for computers at first. E-mail is the fundamental communication tool in the internet network. Actually we Japanese use this even via mobile phones. I heard people in most other countries use SMS as text communication. (Sorry not for sure, see this page!).
In Japan, there's three major company of mobile phones, Softbank, au, and NTT docomo. SMS uses only phone number, but Japanese SMS cannot be sent to other company's phone. So we had to ask e-mail address when you want to text your friends!
But from this summer, we can send SMS to other company's phone! Maybe E-mail address of mobile phones will disappear in Japan! That's needless for every phones!