Why will my voice dial not work?

Hi! I just bought a plantronics voyager legend. Device working perfectly except for the voice dial feature. It is paired with a samsung galaxy S2. When I press the voice dial button and hold for 2 seconds, the prompt to call is not given; instead a short, dull tone is heard.

The voyageur appears to pair with the phone, so if I dial from the phone, I can take the call on the headset however the voice dial feature is not functioning.

Any advice much appreciated.