The Create(Uri) method returns a descendant of the WebRequest class determined at run time as the closest registered match for requestUri. By default, The Create method returns a derived instance of the HttpWebRequest class.
For example, if you create a WebRequest descendant, Handler1, to handle requests to http://www.contoso.com/text/ and another named Handler2 to handle requests to http://www.contoso.com/code/, you can use Create method to return the WebRequest descendant associated with either specified URI.
The .NET Framework in Windows Phone includes support for the http:// and https:// URI schemes. Custom WebRequest descendants to handle other requests are registered with the RegisterPrefix method.
If you attempt to access a file from an FTP site, the application throws NullRefrenceException instead of NotSupportedException.