Paul KF5JIM provides instructions on setting up Asterisk on a Raspberry Pi, and then setting that up to work across a Broadband-Hamnet(TM) (hsmm-mesh(TM)) mesh network.
IMPORTANT UPDATE: Before you unplug the RPi, you are going to need to SSH into the pi, and type "shutdown -h now". Once the lights on the RPi turn off (except the one red light), only then can you unplug the RPi. From my experience, Linux does not do well with unplugging the computer before you shut it down. So with that said, you might need to re-install the system to the SD card. Another regret is not mentioning about installing a fake-hwclock so that Asterisk can boot and continue to run without an active internet connection. You can do this by SSHing into the RPi and typing, "apt-get install fake-hwclock" with an active internet connection.