Siemens Handsfree Headset Adapter Plug from 2.5 mm jacks to Siemens’sConnect any Headset with a 2.5mm standard jack. 2.5mm Jack Adapter. Works with any headset with a 2.5mm jack. 2.5mm jack must have two round rings (most do). Easy to use. Works with any Siemens cellular phones.SIE-C56/ C61/ CF62/ CF63/ A56/ CT56/ S57/ S56/ SL55/ MC60/ M55/ M56/ S65/ S66/ C65/ C66/ CT66/ C70/ C71/ S55/ SX66 and many others.