SitePoint: Silverlight and PHP, Part 2: Creating a Simple Twitter Client
The application that we'll build in this article will allow you to enter a Twitter search term, and display the tweets received in Silverlight. Unfortunately, this process isn't as simple as loading a URL from Silverlight, because of something known as cross-domain access policy.
He talks some about the problem that this cross-domain access can cause for your scripts and how he used PHP to solve it. He created a simple web service that his Silverlight application could query in the same domain. This service did the call to Twitter and returned back the results to the waiting Silverlight app.