The only time I saw a pole-mounted 3ph was in New Hampshire. There, they also seem to put much larger transformers on poles than I would think to (200KVA+) and have been using the insulated primary system with the plastic hangers for a while now. In fact, I think the wire and hangers were invented and manufactured in New Hampshire. IIRC, it had three primary bushings and four secondary lugs.
Never seen a pole-mounted square transformer in use, but there is a PUD on the coast here in Oregon that uses what appear to be clear-coated stainless steel transformers (on the topic of nonstandard pole pigs). None of them seem to be rusting, and all are shiny which suggests that they didn't just have the paint peel off. They look interesting, since pretty much everywhere else has the same old gray ones.
