iPhone trouble assist

HISTORY:

2 days ago, I bought an iPhone 4 for let's say, out of this world, price!
I've always wanted to try an iPhone and since it was a price, to die for, I purchased it.
The guy who sold it to me did not stay around and immediately took off.

So, I started fiddling with My iPhone 4.
Pressed the menu key an iTunes logo and a USB cable flashed on screen with a message :insert a sim card.

Ha, I had not inserted a sim card that is why the flash or so I thought.
Can't get the back cover off, oh bugger, its the tiny pin hole area where to place the sim. Had to Google to find out how to put a sim card in a iPhone, really.

Sim card inserted. Clicked on the menu key, still the same. Pressed, power button, and all hell broke loose. Damn phone is locked. And I DON'T KNOW THE PASSWORD.

My question:

How to get this device working for me?

What are the softwares needed to reflash reset the phone to its original state i. e without any password protection.





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