I had IPv6 only on the default APN configuration pushed by my carrier on Android, last time I checked it And IPv4 only for roaming Both v6 only, v4 only and v4+v6 were supported

For landlines, I'm surprised because some ISPs who were not having difficulties with ipv4 are being the fastest to switch to ipv6. While some who had to deal with CG-NAT and other horrible stuff are fine with ipv4, and haven't yet planned to move to ipv6

Is this due to corporate culture or something ?