I can help you find and use a telephone made for a hearing impaired person. Contact me if you are interested and I will send you my tutorial on the subject. But be aware that this tutorial has nothing to do with physics. I will send it to you (as an attached pdf file, in a private reply), if you ask.
At the age of 81, after wearing hearing aids for about seven years, I finally decided to purchase a special phone for people like me. Hopefully, it will help me understand phone conversations better. A week ago I went to the local Radio Shack store and asked for advice. They said that the cordless Clarity model D-1714 was very popular and I bought it for about $80. This price included a built-in answering machine. Unfortunately the amplification of 40 dB, the highest in the store, was not sufficient, as I discovered during the next two days. That is why I returned the phone and started looking for a better alternative.
Using the internet, I found that Clarity also manufactures phones whose amplifications are 50 dB and 60 dB. The 60 dB alternative (the corded phone XL50) was rejected because it does not have "speakerphone" and "battery backup." Both are important to me. The speakerphone function would allow me to listen via a built-in loudspeaker (without holding the handset). Battery backup would allow me to use the phone when the electric power is off.
The first 50 dB alternative was also rejected; it does not offer "tone adjustment." Such adjustments have important effects on speech recognition. Fortunately, the second 50 dB alternative, Clarity model XLC2, had nearly everything I wanted. Browsing the internet, I found more than twenty comments about it. All but one were positive. All authors of comments appreciated the simplicity of the device. Even the author of the negative comment emphasized simplicity. His complaint was that a visually handicapped person could encounter difficulties. Prices ranged from $81 to $144, depending on the supplier. I purchased the phone for the lower price. The purpose of my essay, is to summarize what I learned about how to use the XLC2. Perhaps the essay will also be useful to others. How can a retired teacher miss an opportunity to teach again?