Today I found this great guidance regarding WCF for Mobile Devices. It is a 72 pages PDF document written by Michele Leroux Bustamante and Nickolas Landry in May 2009.
I recommend that you read this if you are designing/developing Windows Mobile applications that are using any kind of communication.
You can download the document from CodePlex: WCF Guidance for Mobile Devices.
Thank you for sharing Michele and Nickolas!