Dick Smith sell a cheap but effective rider to passenger unit
http://search.dse.com.au/search?p=UK&srid=S2%2d1&lbc=dseau&ts=new&pw=rider%20intercom&pu=25060&uid=979704357&isort=score&w=Motorbike%20Communication&rk=1&sessionid=49271458128d1986273fc0a87e010680
http://search.dse.com.au/search?p=UK&srid=S2%2d1&lbc=dseau&ts=new&pw=rider%20intercom&pu=25060&uid=979704357&isort=score&w=Motorbike%20Communication&rk=1&sessionid=49271458128d1986273fc0a87e010680