Protip: If you want to make 'frappuccino' style blended ice beverages, get your hands on some Xanthan Gum.
It's a powder that serves as a thickening agent (naturally derived, from what I understand) and it will prevent the blended ice and liquids from separating. This way, you get that proper 'slushee' consistency that you get from Starbucks. If you don't add it, you are very likely to find that 5 minutes after blending, you've got a bunch of chipped ice and a bunch of coffee in separate sections of your glass.
Use a pinch of Xanthan gum in your blender - google it if you want recipe specifics, but I think I've done like 2/3rds cup milk, 1 cup strong coffee, a bit of simple syrup, and maybe a cup or so of ice for a completely unhealthy summer treat made cheap.