Abstract: A mouth whistle that is comprised of a plastic card with substantially the same dimensions as a standard credit card, a fold, and registered air inlets that are substantially aligned when the card is folded. The Wallet Whistle can be unfolded for convenient storage. It can be printed with attractive logos, pictures, and/or designs. The card is made of a flexible material that can be repeatedly bent without fracturing along an axis substantially bisecting the plane of said card. The axis of the card may contain a previous fold, crease, score, openings, or a flexible membrane, any of which acts as a hinge to facilitate folding.