I think the use of an RJ31X jack is a good idea. If the ELK panel malfunctions, not likely, you can pull the plug and still have working telephones. The ELK panel only accepts one phone line, so, treat line two like it was your only phone line. If you don't want to use the RJ31X just put your incoming line to the ring and tip on the ELK and use R1 and T1 for your house phones. See page seven of the M1 installation manual.