Separate from phone hardware not being locked to a particular carrier, I'm especially interested in phone hardware not being locked to a bootloader. Currently, Google Pixel hardware units bought through some carriers can't have GrapheneOS installed on them, because that carrier chose to disable "OEM Unlocking" of the bootloader.
Verizon in particular. My Pixel 3 is still more than capable hardware-wise, but it's years out of software support. I could get much more use out of it, but the bootloader is locked and Verizon will not unlock it, so it's e-waste.
My Pixel 3a has started spontaneously shutting down; at any given moment, it may spend an indefinite amount of time in continuous boot-and-shutdown loops that render it unusable.