How to get around the passcode of an iPhone?

I got an iphone 4 free from my job.someone left it there and after a month no one came to pick it up. I want to start using it but there's a passcode. How do i get around it?

You have to do a total restore. You can call Applecare and have them walk you through it or take it to your nearest Apple store. The Specialists have software ready for these type of situations.