The KnowRoaming Sticker SIM works with any size GSM SIM Card, as long as it is not using an adapter or has been cut. We do not support CDMA SIM Cards (Verizon or Sprint) at this time. See this article for more details about why we do not support CDMA SIM Cards.
The KnowRoaming SIM Sticker will work with an inactive SIM Card. It does not need to be attached to a SIM card with an active mobile number or an active phone plan. Pay-as-you-go SIM Cards are also compatible.