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