The Q Card Case from CM4 for the iPhone 4/4S is made from rubber and faux leather. It holds the iPhone securely in place and also provides a pocket on the back side that will hold up to three items (credit cards, drivers license, cash, I.D. card, etc.) Though the cards are held tightly in place, the case has a thumb hole that makes removing the cards quick and easy. The manufacturer recommends that users fit no more than three cards in the card slot, but point out that it will hold one just as securely as it will hold three.
