While Verizon does offer the HTC 10, many users may have one reason or another for wanting to buy the unlocked version, or unlock another carrier's HTC 10 and bring it to Verizon. Normally, there wouldn't be an issue with using a phone in such a manner, but for whatever reason, Verizon has blocked the use of unlocked HTC 10 handsets on their network. Whether you simply obtained your HTC 10 before figuring out you wanted to move to Verizon or you wanted the Carbon Gray version, not offered in Big Red's device stable, XDA user and moderator dottat has you covered. As with any deep-level tweak or fix, this hack is not for the faint of heart, will void the device's warranty and is capable of turning your new HTC 10 into a paperweight, if instructions are not followed carefully.
As a prerequisite, you'll have to use HTC's official tool to unlock the phone's bootloader, then obtain S-Off, which disables some of HTC's built-in security measures. From there, you'll have to decrypt the device. Naturally, all of this ends up involving multiple factory wipes, during which any data you may want to save should be backed up to the MicroSD card. Once you have all of that done, all you have to do is boot into bootloader mode and hook it up to a computer, where you can use fastboot commands to flash the Verizon radio to your device. Once you have the radio flashed, boot up the phone and select the global option in the cellular networks menu, then go into your dialer and enter in *#*#4636#*#*. This will bring up a menu where you can set your radio type; you'll want to set it to "CDMA/EvDOGSM/WCDMA/LTE Auto". You should then have all the basic Verizon functions, including calling, text messaging and data, though a reboot may be in order for some users.
The hack, at this point, lacks most of Verizon's advanced calling features, though the developer community is hard at work to remedy this. It should be noted that going back to S-On status with the Verizon radio on your device could cause the radio to stop working or, more likely, HTC's security measures to declare your device unfit for operation. Obviously, there are risks involved, but if you decided to go with an unlocked HTC 10 and want to use it on Verizon's network, this is, at the moment, the only way to do it.