Another option for some is to allow an additional ringer to be added in a different area of the house or even outside the house. This causes a light to flash whenever the telephone rings. Lights can either be plugged in or are part of the unit. Some attach to the telephone line and others are built right into the handset. They have an adjustable volume control that will make the callers voice louder.
Some models are portable and can be used when traveling.
These headphones plug into a telephone and allow the person to hear with both ears instead of just one ear. They may also have a voice amplifier and volume control. These devices plug into a telephone and a television and allow the people to view each other through on the television screen. This would allow for sign language conversations and also speech reading. The devices do require additional hardware including a video camera and both the caller and the person being called would need to have video capability.