Just finished a FAQ compiling much of the information I've found on this topic as found here on the forum as well as some stuff floating around the web. This post is primarily meant as something for the search engine to find when you're looking through the gear section.
Check it out. http://ducatimonsterforum.org/index.php?topic=25372.0 (http://ducatimonsterforum.org/index.php?topic=25372.0)
keywords:
helmet headset
helmet communicator
helmet speakers
bike intercom