I have Autocom Active Plus -set.
Autocom unit starts as an expandable rider system, which includes the main unit, riders headset, riders
extension lead for bike powered systems, standard phone lead, standard music lead and a basic bike fitting kit.You then have the option to
connect a wide variety of devices: phone, MP3-palyer, bike to bike and passenger, GPS, radar. etc. For bike to bike transmission I have ALAN451R PMR-phones. VOX is working fine.
We (me and my wife) have SHOEI Multitech -helmets, which have factory made places for headsets.
With this equipment communication works with speed up to 140 km/h.
Autocom site: http://www.autocom.co.uk/
Alan site: http://www.alan-electronics.de
Shoei site: http://www.shoei-helmets.com/