Found an iPhone 4 in the street?

Before you say I'm a thief or anything, I've tried every possible way to find the owner, the iPhone screen is a bit cracked on the side but other then that it works, I've had it for about 3 days now and I was wondering if it can be used? There's no pass code, I tried looking for contacts but there isn't any, I just found a voice clip of the owner talkin on it, there wasn't any apps, not music. It was completely empty. I didn't restore it because it's currently running on IOS5 and I don't want to to go to 6.1.1.It's a Rogers phone and I was wondering of its safe to use as a phone?

Well it doesn't have your number programmed into it so you need to call the cellular provider (Rogers). Reset the whole device so you can use it. If you decide NOT to use it, bring it to the Apple store, and they can scan the barcode and see who it belongs too. Every iPhone has a barcode on the back that belongs to the specific owner. Goodluck! & your not a thief, you waited around for someone to claim and they didn't! FINDERS KEEPERS ; )

Take it to apple, they will find the original owner and return it.
once reported lost or stolen it will be useless as a phone.