Differences between RJ9, RJ11, RJ12, RJ45, and RJ48
Source ACCAUC007 rj11 6p4c male to 3.5mm female jack headset adapter cable on m.alibaba.com
Amazon.com: RetailAndBulk (2 Pack) 1.5 Foot Telephone Cord, Professional Grade Made in USA, 6P4C Male RJ11 Plugs with 50 Micron Gold Contacts, Pure Copper Wire Phone Line Cable (18 Inches, Black) : Electronics
RJ11 Connectors And Telephone Interfaces Introduction - AICO