Landline Options for Nighthawk MR1100

Hi all! I am at a loss as to what to do. My parents received a new MR1100 router that replaced an older AT&T model. The older model had a connection for landline, and the new router does not. They no longer have any existing phone jacks in their home and were using the landline through the old router, which worked great. Any suggestions on how I can help them adapt this router to their landline? They use it frequently and also live rurally, so they would need it for emergencies, etc. I’ve seen adapters online, for Ethernet to Landline, but I’m skeptical! Any help would be greatly appreciated. Thank you!