This post is going to be a bit more technical than most people are probably comfortable with, but I'll try to explain it as simply as possible. T-Mobile USA is running an open beta for enabling IPv6 address assignment to some devices on its network in place of the traditional IPv4 addresses.
If you have one of these devices, you can sign up for IPv6 support here right now, change a few settings on your device, and start
rocking testing your IPv6 address as soon as you're approved:
Additionally, if you're in the San Francisco Bay Area, you don't even need to fill out a form - IPv6 is already live here, and you just need to change some settings for it to take effect.