My wife suffered a brain injury several years ago now which has left her needing full time care (from me). Mrs A can't read or write anymore, she doesn't understand money, cooking etc nor does she know where home is until we are outside the door. Her short term memory is very bad, anything learned one day is gone the next. Mrs A watches the same TV programmes several times a week and it's all new each time. My wife is also unable to talk very well and has trouble making herself undestood. I have learned what she is trying to say and I seem to have learned to understand her. However, it's surprising the number of people who don't have the time or patience to wait for her to get words out or make herself understood. I used to watch shop assistants just wave her away if she was trying to ask for a card for me for example. Now I have to buy and write my own cards as my wife used to get so distressed and so did I. Possibly it was a minority - but it was a lot of people! Sometimes we would come across someone who was prepared to spend a little time with my wife trying to undrstand her and that left us both very happy and pleased..
My wife doesn't use the phone as she can't dial numbers (we tried for so long!), she gets very confused and has her speech problems. However, if you do come across someone with a speech impediment Eve you can do nothing better than be patient and let the caller talk in their own time. Let them finish their sentences, don't rush them and then just talk to them as you would anyone else. Please also remember that it takes a lot of courage for them to call in the first place so to just be dismissed by someone impatient is really shattering.