This Thrice SIM adapter allows you to hook two separate SIM cards into the same iPhone. Why would you want to do this? Think about people who regularly travel between countries; now they can keep their USA SIM and UK SIM plugged in, without the worry of dropping, losing or forgetting either while traveling. This Thrice SIM adapter with a iPhone 4 back cover allows you to use your Apple iPhone 4 with two SIM cards. An interface ribbon cable connects the micro-SIM card tray (SIM 1) to a standard SIM card adapter (SIM 2). The dual SIM adapter folds around the back of the iPhone 4 to a place where the case holds them in to position. The back case has a raised area to keep the second SIM card safe and secure and also prevents your iPhone from getting possible back scratches. Now you can switch between SIM cards and handle all your calls on the same phone with this excellent Thrice SIM card adapter.