I would be really surprised if the Sprint didn't include this, as well, but...
I wouldn't say for the HD voice. I've never heard it live, but the demo calls are certainly impressive. Unfortunately, you'll only get this when calling another T-Mobile customer that is also using one of the supported handsets (S III, S 4, iPhone 5, HTC One S, and Nokia Astound) and you both have to be on one of the new towers. They don't even use it for calls to landlines.
Still, it's progress.