After three years, I have finally been able to upgrade the system software on my HTC One M7 (HTC6500LVW) phone from Android 4.2.2 to 5.0.2. I had previously used a Google Play version of this same phone before at a previous job and had encountered no problems in upgrading the operating system to 4.4 KitKat (which was the most recent version of Android at the time). However, whenever I tried to upgrade my current phone from its stock 4.2.2, there was no response. I looked into what it would take to try and upgrade the phone to Lollipop manually, but directions were confusing and inconsistent, often reliant on which carrier the phone was tied to, as well. One thing might work for GSM phones, but not for CDMA phones, et cetera. It was beginning to look like I would need to bypass certain securities and then root the phone before being able to upgrade the software. It shouldn't have been so complicated.
Oddly enough, it was when I was trying to restore an iPhone 5S back to factory settings did I stumble across the solution to be able to upgrade my Android phone, as well. I was erasing and then restoring an older iPhone for testing purposes, but one glitch I encountered was a SIM card needed to be in the device to properly finish the setup process. This iPhone was originally set up on AT&T, but I had a Verizon SIM card available for a similar model of phone, but that did not work, unfortunately. However, I did have a number of other older phones which had originated on AT&T. I first tried the SIM card from an iPhone 4S, but it was larger than the SIM card found on the iPhone 5/C/S models, but I then noticed it was the same size as the SIM card required in the HTC One, which did not have a SIM card since I had purchased the phone from a fire sale clearance.
Curious, I put the AT&T SIM card into my Android phone, which was set up for Verizon. Considering the earlier failure trying to set up the AT&T iPhone 5S with a Verizon SIM card, there were no expectations that this would work, but it was worth trying, at least.
Previous attempts to check for available software upgrades had always failed. I was pleasantly surprised to find that once the phone had a SIM card present that it was able to find software updates. The entire process took several hours since the phone had to upgrade to each to each iteration (Android 4.3, 4.4, 5.0) before stepping to the next version, plus updating any new software that was made available with each update.
All these years I had investigated convoluted methods to upgrade the software and the ability had been available to me all of these years. (sigh). All I needed to do was add the SIM card and it was ready to go.