[Nexus 6P Q&A, Help & Troubleshooting] takoateli:
Guys this is a very difficult one. I really appreciate your help. If there's any place I can get an answer I think it's here.

My Nexus 6P had the Wi-Fi: option in the settings, I saw it many times. However after activating the phone with Sprint (during the process the agent Keith something into my phone which caused it to download and install something from their system) the Wi-Fi calling option is gone from the settings. I've tried everything I can think of to get it back and have been unable to.

I have a very new Nexus 6P running 6.0.1. I purchased this phone especially for its Wi-Fi calling capabilities to use on the T-Mobile network. At the time of purchase there was a lot of conflicting information about Wi-Fi calling coming from T-Mobile's customer support/technical support and numerous support people were saying the 6P is the only phone they were sure would work. I used the phone on T-Mobile's network with Wi-Fi calling and the Wi-Fi calling worked flawlessly, but there were other problems with their service so I moved on to Sprint. Sprint's Wi-Fi calling was horrible, in fact I don't think it was really doing Wi-Fi calling, I think it was just calling to the cellular network. During my time with Sprint I noticed that the phones Wi-Fi calling settings were gone. I contacted Google and they said that if Wi-Fi calling is not allowed by the carrier then the option would not appear in settings. I don't know if that's true but that's what they said. I assumed moving onto Verizon which does offer Wi-Fi calling would restore that option if it was just a matter of having a Sim card which commanded the phone to enable Wi-Fi calling. However after switching to Verizon I still have no Wi-Fi calling settings, and I am unable to make Wi-Fi calls.

In an attempt to get my Wi-Fi calling features back on the phone by factory wiped the number of times from recovery, I also upgraded to android N beta, I also routed the phone and tried installing Cyanogenmod, I also installed pure nexus, I also returned back to the stock Marshmallow, and nothing restored the Wi-Fi calling option on the phone.

I believe what the Sprint agent dialed on my phone to cause it to download and install something from their network is ##72786#, though the agent also dialed ##873283# and ##675#.

One of the Verizon technical support agents suggested that I dial *#*#72786#*#* but when I do that nothing happens except what I dialed clears out of the dialer. I used one of the apps to discover secret codes on my phone and it shows that code is handled by an application called SprintDL. I know some people whose Nexus 6P have never been on the Sprint network also have that application, so I'm not sure if that is something that was installed during the activation process with Sprint.

Now I'm wondering if I need to reflash the vendor information or the radio modem information part of the ROM. It seems like all the roof flashing that I've done would have flashed over everything that could be flashed. But it does seem like something happened to my phone, something was installed or changed or replaced and whatever that is is surviving through multiple factory wipes and ROM flashings.

Sorry for going on, but I want to pass along everything up front so I don't receive irrelevant responses were requests for more information.

I will be so grateful of anybody can help me out of this mess. I live in a place with very poor cellular coverage and Wi-Fi calling is critically important. If I have to send this phone back to Huawei all have to purchase another phone to use in the interim.

Thank you in advance.