If I find an iPhone and bring it in will I be able to use it if not blacklisted

Ideally you should turn it in to the police as it does not belong to you

If someone found your iPhone, wouldn't you like to think that they might try to do the right thing with it which would be to turn it over to local authorities or to return it to the lost and found area in the place in which you found the phone? Maybe somebody realizes that they lost the phone wherever you found it and they are trying to locate it now.