If you expect your iPhone to act as a deck system, that would be a over expectation. But that is not something which can not be achieved! Lil Kikr has released an amplifier for iPhone which can amplify sound up to 10 dB. This device currently supports only iPhone 4/4S.
The Lil Kikr amplifier is like a cylinder and that can be used as an iPhone stand. It can also charge the iPhone. Interestingly this device can also amplify sound that gets into the microphone. This is suitable for recording clear and crisp sound.
To support older devices like iPhone 3G, 3GS and select iPods the company has started another project named Lil Kikr+. Available colors are red, black and silver.