Removing EVERYTHING from iPhone 4?

[zooted]

A few weekends ago I had a party at my house, and an iPhone 4 was left behind. I tried to contact the person who's it was, though I didn't know them. I called a few of the contacts, and no one was any help at all. Anyways, I'm trying to figure out how to completely remove everything from the phone, including the phone number, so that I can either sell it or give it to a buddy of mine. Think what you want of the situation, but it is how it is. Any help is appreciated, however if I'm flamed, congratulations, you've successfully wasted my, and your own time.
I've tried jailbreaking the phone, but it's on 6.0.1, which I don't think is possible to jailbreak at the moment. I also tried to downgrade, but that didn't work either. Again, any help is appreciated.

[blkcadi]

No flaming, but I would really put more effort in finding the owner, calling Apple/AT&T or what ever carrier it was on certainly would give you the info on the owner...anyway.
If the old owner had any sense he would have called his carrier and reported it lost/stolen. That would make the iPhone worthless as the imei would be blocked and not work on any carrier in the US.
You could try to restore it in iTunes and set it up as new to see if it have been blacklisted or not.

[zooted]

It's not been blacklisted. The guy is an idiot, and a very wealthy idiot. By now, he's probably got an iPhone 5.

[Nick_UTD]

Restore it via iTunes and Set it up as a New iPhone, then It's all yours!