The FCC’s Office of Engineering and Technology and the Wireline Competition Bureau (Bureaus) are soliciting comment on expanding their list of key applications and functionalities for which a carrier must demonstrate interoperability when requesting to discontinue legacy voice service pursuant to the FCC’s “adequate replacement” test. The adequate replacement test allows a telecommunications carriers to discontinue voice service when it has established (among other things) that the replacement service constitutes an adequate replacement for the discontinued voice service. Part of this determination includes interoperability with certain low-speed modem devices such as fax machines, home security alarms, and medical monitoring devices. The Bureaus invite comment on whether additional applications and functionalities should be added to the interoperability list in light of various considerations and changes in market conditions and industry developments. Comments are due by November 28, 2018 and reply comments by December 13, 2018.