Tripp Lite Straight Through Modular In-line Coupler Telephone RJ45 F/F - N033-001 - -
Amazon.com: 7' FT Cable Data Modular 8 Conductor Silver Cord Satin Gray Flat RJ45 Telephone Line Flat Cord Voice Data with Plug RJ-45 Connector Both End 8P8C Phone Cross-Wired for VoIP :
RJ45 to RJ11 Converter Adapter, 2-Pack Telephone RJ11 6P4C Female to RJ45 Ethernet 8P8C Male Cable Cord
Uxcell White Plastic Telephone RJ11 6P4C to RJ45 8P4C Connector Cable - Walmart.com