Newer versions of Ubuntu no longer use the /etc/inittab file for configuing getty. A new method is now used called upstart. This requires a file be created in /etc/event.d with the name of the tty device.
Here is a basic example of the contents of /etc/event.d/ttya01:
start on runlevel 2
start on runlevel 3
stop on runlevel 0
stop on runlevel 1
stop on runlevel 4
stop on runlevel 5
stop on runlevel 6
respawn
exec /sbin/getty -L 57600 ttya01
To start getty on the port, run:
sudo start ttya01
To stop getty:
sudo stop ttya01