that has got nothing to do with blocks.

you could have pretty much the same code in any language by doing something like:

    List personList=database.personListForID(id)
    for(person in personList)
    {
        person.setPhoneNumber(phoneNumber)
    }

Personally I prefer that idiom over null checks, it is a lot easier to read. I do like the OP names for 'Finder' vs 'Teller' though, that is a good way to describe the difference, that I haven't heard before.