Can shell login be enabled on the BBB UART?

Does anyone know if it’s possible to change settings so that you can log in to the shell from the UART? Other BBB distros I’ve used have had this, but with Volumio I see kernel messages but nothing more.
It would be handy to have terminal access from something other than eth and wifi. It makes wifi debugging really tricky if all of your steps must leave eth0 alone, lest your terminal go away.