Store brand black handset cord. We have sold hundreds of thousands of cords by this manufacturer. We buy them by the pallet, passing the savings on to you. They are made in China (like nearly all handset cords) and have gold plated contacts. They are lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE free.
Relaxed the curly part of this cord is about 40 inches long, NOT 25 FEET. This manufacturer calls it a 25 foot cord because 25 feet of material is goes into the curling machine. This naming scheme is confusing, but it's the industry standard.
25 foot cords should not be used on desk phones unless precautions are taken. The cord needs to hang by its own weight to keep the coils from tangling. This holds true for any manufacturer. De-tanglers won't help.