If you have an iPhone and a XBOX Live account, get your credit card and buy the $1.99 360 Live application on the AppStore that allows you to check your Gamertag, send/receive messages, add/remove friends, and a lot more. The application is not made by Microsoft or Apple, so helping out the guy who made the App will surely appreciate it.
Check out the full list of updates via 360 Live:
Main Features
* Sign in securely using your Xbox Live credentials. 360 Live automatically retrieves your friends.
* Complete Gamertags management. Add, remove, accept or reject pending requests.
* An organized Friends List. Grouped by status (Online, Offline, etc.)
* Gamer Profile and details including gamerscore, bio, location, country, gamercard, avatar, etc.
* Check your friends complete games history.
* Compare locked and unlocked achievements per game and gamertag.
* Send and receive messages. You can even send messages to multiple recipients!
* Gamercard coverflow style carrousel on landscape mode!
What about PlayStation Network App?