Saw this on the Food Network and realized it would work great for Atkins, just substituted decaf coffee for reg and Splends for sugar.

2 cups strong black coffee sweetened with Splenda
1/2 cup heavy cream

Pour coffee into shallow pan and place in freezer.
Check every 1/2 hr and if there are ice crystals scrap them into the coffee with the edge of a spoon. After about 2 hrs you will have coffee that resembles shaved ice .

Whip the cream (with a little Splenda if you like)

Layer the coffee ice and whipped cream into a tall glass, start with coffee and finish with cream and top with a little grated chocolate(Hershey's Sugar Free Bar)

I served this to company in champagne flutes with long ice tea spoons and everyone raved about it, didn't even know it was "diet" food.