Facebook released Facebook Messenger for sending and receiving messages between Facebook friends. This facebook app supports group messaging, location update (which your friends can see your location map, you can turn off this feature), messages directly delivered to your friends mobiles instantly. App available for Android and iPhone devices, soon available for blackberry, but no word about Nokia Devices for this official app.

Get the app from https://www.facebook.com/mobile/messenger

Pros

Free
Ability to send SMS texts in addition to instant messages
Multiple settings for push notifications

Cons

No list of friends online
Profile pictures of friends missing when using SMS
Some messages received in duplicate.