Amazon.com: NECABLES 2Pack Short RJ9 Cable 1ft 4P4C Phone Cord Telephone Cable RJ9 / RJ10 / RJ22 4P4C Male to Male Straight for Both Data and Voice Black - 1 Foot : Electronics
Converter Adapter | Converts RJ-9 to 2.5mm for phones that have a 2.5mm jack., (2200-11095-002) | Use with APP-50, APP-51 EHS for Polycom, Connecting telephone devices to 2.5mm headset mini jack
2 Pack) Black RJ9 4P4C Straight or Reverse Cable. Custom Size From 2" - 10ft | eBay
Jabra RJ-9 to RJ6 Headset Cable, Black, 0.5m (8800-00-101)