Use Compression

You can reduce network bandwidth requirements by employing a compression scheme, such as gzip. Using compression is even more important when using an XML-based format like Atom. You should consider using compression to reduce the network requirements when you use the OData client for Windows Phone, which only supports the Atom XML format.

Implementation

Enable compression at the server, and make sure it is configured for the MIME type of the response from your service (such as application/json or application/atom xml). For more information, see the post on IIS Compression in Windows Azure. To request a compressed response from the web server, set the Accept-Encoding header in the request to the supported compression scheme, such as gzip. Windows Phone does not currently have its own compression library, so you must use a third-party compression library, such as SharpCompress. The OData library for Windows Phone enables you to set the headers to request compression. It also provides an API to access a compressed response stream and return the decompressed response for the library to materialize into objects. For an example of how to use compression with the OData client for Windows Phone, see the article OData Compression with Windows Phone 7.5 (Mango).

The using Windows Phone on Azure page mentions using SharpCompress for the GZipStream. I guess no one else has bothered compiling the GZipStream into Silverlight/Windows Phone 7 :)