Find the owner and send it back.

Find the cell number, and call it from an activated phone. Chances are they kept the number. Say that your company has been trying to find the owners for the past 3 months and ask where they would like the phone sent to. They might say just keep it, if they had insurance on the phone.

But any Verizon place will do it for you. When I bought a replacement phone on eBay they activated it and reset it for me.