iphone, disappearing voice control!

[lady topaz]

I have had a 3GS for a few weeks now. Initially I had a voice control icon and I had fun playing around with it. Just went to show someone only to find the icon has vanished. I tried pressing the control button and the voice control screen comes on but doesnt recognise any imput from the phone book. It just repeats any old name at random.
Any clues?