I hate to cross-thread post, but you seem to know your stuff... how does the Sprint model work, as it too is a CDMA network?
Coincidentally, I also worked for Sprint. But everything I've said is pretty much common knowledge. It's the same as the Verizon as far as I know. Only difference, which I picked up from reviews, is that it uses an actual SIM instead of an embedded SIM like all other Sprint phones. But again, that's only for LTE purposes.
Now, a Verizon HTC One will most likely work on AT&T (since Verizon phones aren't allowed to be locked, as part of an FCC agreement in exchange for being allowed to use the 700 MHz band of LTE spectrum). But Sprint usually has manufacturers block out US-based SIM cards, even if the device is unlocked. This was the case with the iPhone 4S, 5, and all other Sprint SIM-capable devices.
TL;DR: Sprint is the same.