I don't have the Icon (I'm on T-Mobile), but I do have the Lumia 810, 920 and 925. I never used a case on the 810 because that thing was super grippy. I have cases for my 920 (first one I ever got was the Incipio dual pro, which is excellent and protects the phone all over). For my 925, I only have an Incipio feather case. I'd say if the phone feels grippy enough without a case, don't get one. If it's more slippery, however, I would definitely say get a case.