Come to rural western Ohio, where the only non-dial-up options, in some places, are super-high latency satellite and a local "WISP" who NATs their whole Customer base into what appears to be a /29 (your "public" IP assigned by their CPE lands in 10.0.0.0/8).
NAT and double-NAT are common in WISP networks. Also of course most hotels, Starbucks, schools, conferences, airplanes, albeit those are not ISP services. And cellular carriers often NAT.
You only get one, so you typically NAT everything, port 25 is blocked and often port 80 is as well, but that's about it.