I'm on the last developing phase of a social networking app for iOS that has a chat module. Right now I'm trying to figure out the best way to achieve these features:

• Send message instantly to another user. If other user is online, delivery should be instantly.
• If user reads the message, the remitent should be notified of that action.
• If a user visits my profile, I should be notified instantly.

What would be, in your opinion, the best approach to achieve that experience? The server is CentOS 5.6. I've previously reviewed XMPP, sockets, but I'm still unsure on what the best approach is.

Any opinions and resources will be much appreciated.