Plantronics m3000 bluetooth headset

hi i have got a plantronics m3000 headset and i have successfully paired it with my playstation 3, but when online on call of duty 4 i cannot seem to get a connection. some people have talked about it having to be "open mic" but what is this ? and how can i get my headset up and running for online gaming

if you could please email me on -

sitonmyface_88@hotmail.co.uk

it would be much appreciated..... thankyou

scott rose