I don't mean one of the bulky, fold open type. I mean like these:
Amazon.com: Speck SPK-A0332 CandyShell Card Phone Case for iPhone 4 (NightDrive Grey, Fits Verizon and AT&T Models): Cell Phones & Accessories
Amazon.com: CM4 Q4-BLACK iPhone Wallet Card Case for iPhone 4/4s - 1 Pack - Retail Packaging - Black: Cell Phones & Accessories
Amazon.com: Speck SPK-A0332 CandyShell Card Phone Case for iPhone 4 (NightDrive Grey, Fits Verizon and AT&T Models): Cell Phones & Accessories
Amazon.com: CM4 Q4-BLACK iPhone Wallet Card Case for iPhone 4/4s - 1 Pack - Retail Packaging - Black: Cell Phones & Accessories