Sure, there are any number of phones with dual SIM card slots, most of them built for Asian markets, but the iPhone 4 is about the furthest thing from dual SIM: in fact, it doesn't even have one Big Person SIM to call its own. Luckily, USBFever has a hacktastic solution to this problem (a followup to their iPhone 3G version), with a new $30 case that can host dual full size SIM cards on the back of an iPhone 4 (entombed in some classy clear plastic, naturally), while running an adapter to the iPhone 4's micro SIM slot. You can then switch between the two SIMs from the iPhone's own settings menu, though unfortunately you can't rock both SIMs simultaneously. Looking for a more DIY approach? Bust out your X-Acto and check out our SIM resizing guide!