T-Mobile, Verizon, Sprint, US Cellular, and AT&T were all part of the original agreement. In an email to The Verge, a T-Mobile spokesperson posted its policy and said the company had adjusted to the rules "in advance of the deadline," and Verizon said it was also compliant, linking to its official rules. US Cellular's written policy still says it's working towards the goal, but the company said it had met all the CTIA's obligations as of today; Sprint also said its own standards would "meet fully" with the CTIA's today. AT&T hadn't responded as of this writing, but its policies generally match the agreement.
If you don't want to go through a carrier, of course, you can handle the the process yourself or through a third-party company. That's the beauty of a law President Barack Obama signed last August, putting the copyright exemption back in place for another few years. But for most people, carriers are still the simplest path to unlocking — and over the past year, that path has gotten quite a bit smoother.