A stock rooted HTC One M8 2.16.651.4 ROM has been released for the Sprint HTC One M8 varients along with the firmware for the ROM. Additionally there’s the 2.16.654.4 images if you want to use the Harmon Kardon audio versions of the ROM and separate flashable firmware.
I’m not sure if the HK versions of the ROM also include WiFi calling, but considering the finishing version number is the same, it probably is.
If you’re currently running a custom ROM and like it, probably you should wait to play around with this until your ROM’s developer gets a chance to incorporate the new 4.4.3 and WiFi calling modules into their ROM codebase.
The enhancements to the ROM are listed as WiFi calling, HD Voice icon, and bumping the Android version up from 4.4.2 to 4.4.3, so unless you absolutely need WiFi calling or something that’s in 4.4.3 there’s not a particularly compelling reason to be the first to beta test Sprint’s new software.
It should be noted that the .4 versions seem to have appeared for both the One M8 and the Harmon Kardon Sprint One M8 at the same time. I’d been asked about whether that would happen on Twitter and @sprint said no.
@mattregul No, the updates will not be released at the same time. *LS
— Sprint Care (@sprintcare) July 6, 2014
So unless Sprint and HTC are doing odd version numbering and not giving the HK edition the WiFi/4.4.3 now that seems to be wrong, which is what I told Sprint Care and the person who asked on Twitter.
Whatever the case, the ROM and the firmware bundles for both are now available for download. Remember though flashing any firmware bundle could result in some issues, so unless there’s a need you might want to wait on that for a bit.