Plug into the 2.5mm headset jack on your cell phone or cordless phone, put your hearing aid on the telecoil setting, and the sound from the phone will be transmitted to your hearing aids. An affordable, easy to use solution for hearing on a mobile phone. No batteries to worry about. Just plug in and go. Begin and end calls at the push of a button. Standard 2.5mm plug with an adapter for use with a Nokia phone. 90 day warranty.