This is the bottom cable that connects Plantronics H-series Headsets to these specific Aastra/Siemens/Mitel IP phones:
Aastra 5370, 5370IP, 5380, 5380IP, 6771, 6773, 6773IP, 6775, 6775IP, 7434IP, 7446IP
Mitel 6865i, 6867i, 6869i, 6871, 6920, 6930, 6940
Siemens OpenStage 40/60/80