Some hearings aids have a special feature called a telecoil, which allows the sound from a telephone or other sound source to be sent directly inside the hearing aid for customized amplification. Connecting via telecoil also helps to limit the impact of background noise on the listening experience. Another name for a telecoil is t-coil.
A specialized type of headset may be needed in order to make the most of a telecoil enabled hearing aid while using a telephone. An audiologist or other may be helpful in determining whether or not a particular person is using a telecoil enabled hearing aid and would benefit from a telecoil compatible headset. You can also contact a hearing aid manufacturer or distributer for information on the features of the hearing aids that they carry. It is best to have the brand name and model number handy when inquiring about the features of a hearing aid.