J sees the phone box

For a while now, J has been asking me and L what the large metal boxes are that he sees around sitting on the sidewalk.  I've told him I thought they were for phone lines, but of course this doesn't make much sense to him.  Yesterday on the walk to his preschool, we walked by a box that was opened by a technician working on it.  We stopped to watch him making connections and re-organizing the bundles of wires.  I tried to tell J about how, when he talked on the phone, electricity carried his voice down the wire, through some switches and along another wire to someone else's phone.  The technician was very nice, and told J that if this box was knocked over, thousands of phones around there would go out.  J said he didn't understand that, so I restated, "If a big truck comes and knocks this box over, thousands of phones in the buildings around here would stop working."  This seems to have impressed him.  He didn't say much while we were looking at it, but as we walked away, he said, "Wow, that was amazing!"