Gmail's not just for email--you can also communicate with your friends in real time using chat in Gmail! Gmail is part of Google's chat network, which means that you can communicate with your friends using iGoogle, orkut, and Google Plus.
If you're already using Gmail, all you need to do to chat is sign in, invite your friends, and start a chat. If you'd like to try Gmail, it's easy to sign up!
Voice and video chat in Gmail
In addition to instant messaging, you can also chat face to face with up to nine people and call phones. Learn how to make voice and video chats.