I\'m developing a Windows Phone 7 app but don\'t want to re-implement my own identity / authentication service - espcially when we know the user will be signed in with a Win
Have you looked Windows Live Messenger Connect? It recently came out of Beta (announcement). Windows Live Messenger Connector provides Javascript and REST APIs for applications to use the framework, here is the starting point for the documentation. You can use the Windows Live REST explorer to explore the REST API, there is a sample desktop application that shows how to integrate Windows Live Messenger Connect.
HTH, indyfromoz