NVRAM Testing: You can test if your NVRAM is working by running the following Terminal command and rebooting: `sudo nvram TestVar=HelloWorld`; once you reboot, run `sudo nvram -p | grep 'TestVar'`; if you see a result, your NVRAM is working; if not, your NVRAM is broken and needs to be fixed, or otherwise iMessage won't work; after testing, you can delete the TestVar variable by running `sudo nvram -d TestVar`