Amazon.com: kenable ADSL Broadband Modem Cable RJ11 to RJ11 Black 1m (~3 feet) : Electronics
Amazon.com: RJ45 to RJ11 Cable, 6 Feet Phone Jack to Ethernet Adapter RJ11 6P4C Male to RJ45 8P8C Male Connector Plug Cord for Landline Telephone : Electronics
RJ45 and RJ11 - YouTube
Customized rs232 db9 to rj11 rs232 to rj12 rj9 rj25 rj45 serial cable DB9 female to RJ11 4p4c Cables 1M _ - AliExpress Mobile