Dog tag with phone number - very smart. I have called many owners on my walks, very nice to be able to help them find their dog again and reunite them. All though they should take care of their dog and make sure it cannot run away in the first place (I especially hate loose dogs, since you never know how unstable they are, and I especially dislike meeting them when I'm with my kids).
The rules where I live is very strict, I follow them with my dog, so I expect others to do the same, but there's always someone who does not give a shit.
It's not because of the owner I call, it's because I want the dog to be safe, I could not care less about the owners really.