USB Fever has released the TRI-SIM Card for iPhone 4G with Black Back Cover
(http://www.usbfever.com/index_eproduct_view.php?products_id=2006).

With the US$39.99 add-on card, you can have up to three SIM cards to be installed in your iPhone 4G. It also comes with a crystal case to protect the Tri-sim card and the Apple smartphone.