USBFever is in the thick of things with their 3-in-1 External Battery case with Dual SIM function that caters for the iPhone 3G and iPhone 3GS. This case will boast a built-in 1900mAh battery, alongside a mini-USB port for recharging, while offering open access to all ports and controls although you won’t be able to use the Dock Connector and ring/silent switch. An LED power indicator comes in handy to let you know just how much juice is available, while the dual SIM card adapter will give you the ability to switch between lines via a Settings application – no idea on whether the adapter is compatible with non-jailbroken/unlocked iPhones though. Expect this nifty device to go for $60.