AFAIK, IMEI no. can't be changed. It's embedded into the mobile hardware itself. Though, there are reports that IMEI can be programmatically changed, but everyone can't do that. and moreover, it's illegal. I'll suggest, there might be some numbers saved on the handset, try calling one of them, try informing the owner, and return it. He/She'll be thankful to you. In case it gets traced(?), and you're found in possession of that device, you might get jailed. No one would believe that you found it lying on the road, and you haven't stolen it.