the phone in a drawer solution works basically by default on apple devices. Very common solution in outback Australia (satellite internet only, no phone coverage)
Just thinking aloud here - would you need to disable all automated updates on iOS before doing this, lest the device do a reboot for a system security update, and end up on the lock screen?
There's probably some interesting failure modes when trying to get a modern device to stay connected for months on end, without deciding to reboot for a security patch or similar, or taking an automated app update.
I always have to enter the password to start an install. I’m not sure if there’s a failsafe after some period of time since I usually install day-of but I usually wake up to some nag saying it couldn’t be installed overnight because I didn’t authenticate, and all of my devices are set to install automatically.
Note that there is a difference between regular "locked" and the "locked" after a reboot. For the later most of the disk is still encrypted so very little data and few services are operational. You can likely recieve text messages but I doubt much of iCloud syncing works.
So with forwarding on, if you receive a garden variety SMS (green in iMessage) it will forward on as a normal (blue) iMessage over IP to other iOS devices on the same account?
yes. it comes up green, but is delivered to all other same account iCloud devices. you can reply too, and it works it out. I send and receive SMSs via my MacBook and iPad.
There's probably some interesting failure modes when trying to get a modern device to stay connected for months on end, without deciding to reboot for a security patch or similar, or taking an automated app update.