I call a patient and get her answering machine:
"You have reached [name]. You can leave a message but you must speak very loud and very slow. I do not hear well, so you need to talk very clear. You can spell things, but I do not spell well, so I may not understand. You should also call back when I am here, since sometimes I forget to check the machine. If this is my daughter, I can't hear you when you call from the car. Everyone should wait for the machine to do a beep. Thank you for calling."
I left a message, but I guess I'll probably try her again tomorrow.