Call Caption telephones

[nebo113]

Because my cousin has boundary issues (as in the lack of), she sent my mother a "call caption" telephone unit, without consulting with me first; it comes with a screen

My almost 96 year old mother wears hearing aids, but still has difficulty, particularly on the phone.

From what I can gather from poking around the internet, the FCC picks up the cost, IF the user has hearing issues.  However, one source said the user "self-qualifies" and nowhere can I find the criteria for qualifying.

Another concern is that a third party listens to conversations and "captions" what the callee is saying.  I assume that the captioning function can be turned off when Mother is making calls about sensitive matters such as health or finances.  Again, however, I cannot find that info online.

I assume that the instructions that come with the phone contain this information, but Mother, while still functioning quite well, might not quite understand it.

Has anyone had experience with "call captioning" phones?

Thanks.