Sure, we’ve seen many phones with dual SIM card slots. Most are for the Asian markets, but the iPhone 4 is not one of them. Well, USBFever has come up with a solution to that problem, with a new $30 case that can hold dual full size SIM cards on the back of your iPhone 4.
It holds the cards in place and runs an adapter to the iPhone 4’s micro SIM slot. You can then switch between the two SIMs from the iPhone’s settings menu, though you can’t use both SIMs simultaneously.