[danyork]

Some of the carriers who have gone IPv6-only like T-Mobile USA use technologies like 464XLAT to access IPv4 sites. Here's some info:

http://www.internetsociety.org/deploy360/resources/case-stud...

And RFC 6877 specifies 464XLAT:

http://tools.ietf.org/html/rfc6877

and here is even more detailed info from T-Mobile:

https://sites.google.com/site/tmoipv6/464xlat

Regarding DS-Lite, this video from RIPE NCC provides a nice overview:

http://www.ripe.net/lir-services/training/e-learning/ipv6/tr...

Both DS-Lite and 464XLAT are ways that an ISP can be IPv6-only yet still access legacy IPv4 content and services.