EPOS Sennheiser ED CSTD 01 RJ11 Adaptor and Cable for Wired Headsets | 1000836
Cable for Heil headsets 3.5mm jack to 6p6c modular RJ11 for Yaesu FT-7800 etc | eBay
1PC Phone Adapter rj11 to 3.5 female Adapter Convertor Cable PC Computer Headset Telephone - AliExpress
RJ9 Male to 2 x 3.5mm Female Jack Headset Phone Mic Audio Splitter Ada
Headset Doubler Training dual plug for Training Headsets – Headsets4business
VoiceJoy RJ9 Headset Adapter Extension Cable- Female 4P4C to Male 4P4C Cable, not RJ11/RJ12, for Plantronics, Jabra, Hot Desking Office Phones : Amazon.co.uk: Electronics & Photo
VoiceJoy Headset Adapter/Converter VoIP 2.5mm Headset to RJ9/RJ10 Plug ONLY for Cisco Phones,Cisco 794X 797X 796X 88XX 99XX Series : Amazon.co.uk: Electronics & Photo
Headset Adapter Cable Ethernet RJ45 8P8C Male Plug to RJ11 6P4C Female Socket | eBay
Headset Buddy Training Adapter Twin RJ10 Sockets & Mute Button
RJ11 to BT Adaptor - The VOIP Department - Your eco telecoms supplier