Found iphone, how do I return? If not, how do I keep?

Back in August, I found an iPhone 4 on the ground. It was grimey and the protective case was grimey too. I just found it under some bushes in a neighborhood.

I tried turning it on. No charge. I took it home and showed it to my brother. He was a technician in a shop that worked on smartphones and laptops.

We charged it, then when he took a look at it, he said it was no longer in service and that whoever owned it probably cancelled their service on that phone. I'm not sure, but I think it's an AT&T phone, and it has one of those SIM card things.

He told me to look up on youtube how to restore it, which resets it, basically like new. Confident that my brother knew what he was talking about, I did. I've never owned a smartphone before and I don't really know much about smartphones, so I cleaned it up and kept it.

So far, I've just been using it to get wifi, but my brother says I should get it "jailbreaked" and "unlocked".

I trust my brother, but a few months after finding it, I'm wondering now: Was there a way to find the owner?

Will the carrier ACTUALLY get it back to the owner or will they just strip it for parts or restore it to resell it?

Are there websites where people put up notices for lost iPhones?

If I am unable to find the owner, how do I go about "jailbreaking" and "unlocking" this phone? I'm going to be out of the country and will be in need of a functioning phone as I go from one place to another.