Facebook unveiled a new email-based messaging based service to its 500 million users, putting it in more direct competition with established giants Yahoo! and Google. 

In a press conference, Mark Zuckerberg, Facebook's CEO, said the new messaging system isn't an email killer, but will be able to handle email and host of other communicative systems including instant messaging and SMS text messages. Facebook Messages will also eventually allow users to get a Facebook email address (@Facebook.com).

It's not e-mail. It handles e-mail in addition to Facebook messages, and Facebook IM, and other IM and SMS and all the other different ways that you want to communicate. It's true, people are going to be able to have Facebook.com e-mail addresses, but it's not e-mail, Zuckerberg said.

The messaging system essentially would take emails, IMs and SMS and put them into one blended  interface. Users will be able to communicate with each other using whatever medium they prefer, even in real time. It will track every single message two people send each other and be able to prioritize the people that are more important in a user's life.

Unlike traditional email, there will be no subject lines, or CC'ing. Messages will be sent when a user simply hits the enter key to send one. Zuckerberg said it's an evolution of traditional email, which he said has become too slow and too formal. He was inspired, he said, by a group of high schoolers who said they do not even use traditional email for that very reason.

E-mail is too formal, Zuckerberg said. Think of the friction of trying to think of the e-mail address and think of a subject line, write 'Hey Mom,' at the top and 'Love, Mark' at the bottom.

Zuckerberg said Facebook has been developing the new service for 15 months.