Yeah, the "red box" stuff was legit, it's just that A. few payphones seem to even exist anymore, and B. the ones that do are mostly COCOTs, not Telco operated phones that are (or were) susceptible to red-boxing.
Yeah, but you can op divert COCOTs or just hack them directly (one of my schools' COCOTs had a flaw where you could make the modem think you were still operating for free after dialing toll-free if you hadn't hung up the phone completely, rendering free unlimited calls)
Even better, you can just beige box off them if you can find the demarc point, which is usually on the backside of the building where the phone is. Since all the "magic" that makes it a "pay" phone is in the phone itself, the line it's hanging off of is just a plain old phone line, with full toll call ability and everything.
Back in the mid 90's, when I was a little bit into the phreaking scene, me and my buddies used to always beige box off of a COCOT to dial into the modem for the local phone switch, so we could play around. We found a payphone at a gas-station halfway in the middle of nowhere that closed fairly early, so we'd just pile my laptop in the car, drive out there, park about 40 feet from the phone, run a long ass cable to the demarc box and then sit in the car and hack/phreak. Good times... :-)