This tutorial worked for one evening. The following day, Ubuntu upgraded and this system no longer worked.

Enable airpods as headphone

Edit the ControllerMode to bredr from the default value of dual

sudo emacs /etc/bluetooth/main.conf

Then restart the Bluetooth service using

sudo /etc/init.d/bluetooth restart

You should now be able to pair your airpods and use them as headphones.

Enabling airpods as microphone

1. Install ofono using

   sudo apt install ofono

2. Configure pulseaudio to use ofono

   Go to /etc/pulse/default.pa

    Find the line `load-module module-bluetooth-discover` 
   
    Change it to `load-module module-bluetooth-discover headset=ofono`
   

   Add the user pulse to the group bluetooth to grant the permission

   sudo usermod -aG bluetooth pulse

   Add the folowing line to /etc/dbus-1/system.d/ofono.conf before </busconfig>

   <policy user="pulse">
       <allow send_destination="org.ofono"/>
   </policy>
   

3. Provide a "modem" to ofono by installing ofono-phonesim

   sudo add-apt-repository ppa:smoser/bluetooth
   sudo apt-get update
   sudo apt-get install ofono-phonesim
   

   Configure phonesim by adding the following lines to /etc/ofono/phonesim.conf

   [phonesim]
   Driver=phonesim
   Address=127.0.0.1
   Port=12345
   

   Now, restart the ofono service with

   sudo systemctl restart ofono.service
   

4. To run ofono-phonesim -p 12345 /usr/share/phonesim/default.xml on startup, create the file /etc/systemd/system/ofono-phonesim.service and add the following content.

   [Unit]
   Description=Run ofono-phonesim in the background
   
   [Service]
   
   ExecStart=ofono-phonesim -p 12345 /usr/share/phonesim/default.xml
   Type=simple
   RemainAfterExit=yes
   
   [Install]
   
   WantedBy=multi-user.target
   

5. Now, you need to put the modem online. Do this by cloning the following github repos

   cd /tmp
   git clone git://git.kernel.org/pub/scm/network/ofono/ofono.git
   git clone https://github.com/bryanperris/ell.git
   

   Once you have these repos, cd /tmp/ell and run the following commands.

   autoreconf -fi
   ./configure
   sudo make
   sudo make install
   

   Now, cd /tmp/ofono and run the following commands

   autoreconf -fi
   ./configure --enable-external-ell
   sudo make
   sudo make install
   

   If there are any D-Bus errors, install the following

   sudo apt install libdbus-1-dev libudev-dev libical-dev libreadline-dev
   

   Now move the ofono/ and ell/ directories to the /opt/ directory.

   mv ofono/ ell/ /opt/
   

   Now you can put the phonesim online by creating another systemd unit file that depends on the ofono-phonesim. Put the following content in /etc/systemd/system/phonesim-enable-modem.service

   [Unit]
   Description=Enable and online phonesim modem
   Requires=ofono-phonesim.service
   
   [Service]
   
   ExecStart=/opt/ofono/test/enable-modem /phonesim
   ExecStart=/opt/ofono/test/online-modem /phonesim
   Type=oneshot
   RemainAfterExit=yes
   
   [Install]
   
   WantedBy=multi-user.target
   

6. Run both daemons with the following commands

   sudo systemctl daemon-reload
   sudo systemctl enable ofono-phonesim.service
   sudo systemctl enable phonesim-enable-modem.service
   sudo service phonesim-enable-modem start
   

   You can check the status of the modem with

   sudo service phonesim-enable-modem status
   

   Lastly, restart pulseaudio with pulseaudio -k

For the modem to be online, you must have ofono-phonesim -p 12345 /usr/share/phonesim/default.xml running in a shell.

References

https://reckoning.dev/blog/airpods-pro-ubuntu/

https://askubuntu.com/questions/1204810/make-no-rule-to-make-target-ell-util-c-needed-by-ell-util-lo

https://askubuntu.com/questions/506116/bluez-installation-configuration-error-for-dbus-1-6

bluez/bluez#125

https://askubuntu.com/questions/1283580/ofono-enable-modem-fails-with-dbus-exceptions-dbusexception-org-ofono-error-fai