Its basically just stuck in the ice cream, its generally not a full size flake, though I have used them before, you can get the gist from this link:

http://www.cadbury.co.uk/EN/CTB2003/.../ice_cream.htm.

The Flake 99 is on the left. Putting it in the ice cream made it less likely to melt (obviously) and also more brittle so it flaked easier, brilliant for getting chocolate all over your clothes. I used to use the flake as a spoon and prolong it for as long as possible.

The blurb below also tells why it is called a 99, you learn something every day!

I think McDonalds may have done a Flake McFlurry with the Flake broken into the Ice Cream, I know they have definitely done a Creme Egg McFlurry and a mini-egg McFlurry. McFlurry ice cream is not my favourite though.