For it to be possible to hard brick a phone, some of the software the phone has to run to boot and flash itself -- something from the point where it's a just-powered-on processor running address 0 to the point where the phone is writing a new image to flash -- needs to be itself in flash that the phone can write. Usually this is something like a secondary boot loader. If you erase that, then you can't reflash anymore. Hard bricked.

On a phone where you can write something new with only the aid of whatever software is in ROM that the phone can't write, whether or not it's by shorting a couple of pins and there's USB straight into the processor, you can't truly "hard brick" the phone. Unbricking would always be possible at least in theory, provided you can feed it the firmware in whatever format it needs.

For it to be possible to hard brick a phone, some of the software that the phone has to run to boot and flash itself -- something from the point where it's a just-powered-on processor running address 0 to the point where the phone is writing a new image to flash -- needs to be itself in flash that the phone can write. Usually this is something like a secondary boot loader. If you erase that, then you can't reflash anymore. Hard bricked.

On a phone where you can write something new with only the aid of whatever software is in ROM that the phone can't write, whether or not it's by shorting a couple of pins and there's USB straight into the processor, you can't truly "hard brick" the phone. Unbricking would always be possible at least in theory, provided you can feed it the firmware in whatever format it needs.

For it to be possible to hard brick a phone, some of the software the phone has to run to boot and flash itself -- something from the point where it's a just-powered-on processor running address 0 to the point where the phone is writing a new image to flash -- needs to be itself in flash that the phone can write. Usually this is something like a secondary boot loader. If you erase that, then you can't reflash anymore. Hard bricked.

On a phone where you can write something new right from USB into any of its flash memory, with only the aid of whatever software is in internal ROM, by shorting a couple of pins on the processor, you can't truly "hard brick" it. Unbricking would always be possible at least in theory, provided you can speak its USB protocol and send it new firmware in whatever format it needs.

For it to be possible to hard brick a phone, some of the software the phone has to run to boot and flash itself -- something from the point where it's a just-powered-on processor running address 0 to the point where the phone is writing a new image to flash -- needs to be itself in flash that the phone can write. Usually this is something like a secondary boot loader. If you erase that, then you can't reflash anymore. Hard bricked.

On a phone where you can write something new with only the aid of whatever software is in ROM that the phone can't write, whether or not it's by shorting a couple of pins and there's USB straight into the processor, you can't truly "hard brick" the phone. Unbricking would always be possible at least in theory, provided you can feed it the firmware in whatever format it needs.