Xbox LIVE has released the official Xbox LIVE app for iOS owners. This is a universal iOS app.
This free app will allow iOS owners to stay connected to the Xbox LIVE community when they are away from their Xbox 360 game console.
Through the new app, users will be able to read and send messages to their friends, manage their friends list, invite new friends, read and Edit their full LIVE profile (name, bio, motto), change their avatar features/items with the avatar closet and view and compare their achievement progress with friends.
You can download the free app here
Microsoft has already introduced the Xbox Companion for Windows Phone 7, which has even more features than the iOS app. You can download that free app here