Here is a new dual-SIM case for iPhone 4 that supports dual standby and doubles as a power pack. After you attach the battery case to your iPhone 4, you will have two SIM card slots – the original Micro SIM slot of the iPhone 4 and a mini SIM slot on the case. Compare to another dual SIM case, the new case supports dual standby, meaning both SIMs are active at the same time.
In order to use the secondary SIM for phone call, you have to jailbreak your device and install an app. However, you can only use the second SIM for SMS and phone call and caller display is not available for second SIM. The case has built-in 800mAh battery. It comes with a micro USB cable for charging and a bumper. It is priced at $249.99.