Amplified telephones are designed for people with hearing loss but many have added features that are helpful for manual dexterity issues and poor vision.
You will see many of the Amplified Phones corded, cordless and mobile in this website that are hearing aid compatible. Hearing aid compatible also includes cochlear implants. Both the hearing aids and cochlear implants must have the telecoil / loop setting activated as this allows them to work with the inductive coupler that is built into the "ear" end of the handset.
The amplification varies with different models and is there to provide options for severity of hearing loss. For example someone with mild hearing loss does not require a phone with adjustable amplification to 60dB. Equally a person with severe hearing loss will receive little or no benefit from a phone with adjustable amplification to 30dB. There is also the cost implication as the greater the amplification the greater the cost.
There are many common features on the telephones such as volume control, tone control, adjustable ringer control, speakerphone, flashing ring indicator light and memory functions for emergency calls.
The big buttons assist people with manual dexterity issues.
To assist with poor vision there a phones with combinations of big buttons, larger sized numbers, screen contrast and bright light visual ring indicator.