Who's on First?

Quick update: 

My grandmother is now 82 and her mind is going. I always assumed her body would begin to give out first, but what's scary is she's in pretty decent shape physically. Having a conversation with her on the other hand, is challenging to say the least.

A good example of what a conversation with my grandmother is like nowadays is the classic Abbott and Costello routine. Who's on first? No, what's on first? What? I thought you said who? etc. Take this recent conversation:

We were on the phone and she asked for my sister's phone number. I told her I would call her with it when I got home.
Note: numbers, addresses, and uncommon words of any kind can no longer be successfully conveyed to Gan over the phone. 
Me: "Hi Gan. Okay, I'm home,"
Gan: "Hi. Can you give me that address?"
Me: "Address? I thought you wanted to phone number?"
Gan: "No, I've got the phone number, I need the address."
Me: (Knowing good and well she asked for the phone number, but any attempt to argue or rationalize is futile) "Oh, okay. Do you have a pen? Alright it's 1305 17th Str-"
Gan: "Wait, wait. You're talking too far away from the phone. Say that again?"
(Mind you I'm already speaking slowly and yelling.)
I repeat it twice, and each time, when I get to the street name - 17th - she says "Sedington Street? Cedar Tree? Second Street?" Basically anything but 17th Street.
Me: "Okay Gan, let's start again. You've got 1305 right? Okay now write one seven the street is called one seven."               Gan: "And that's all? Well that ain't no number..."               Me: "What?"                                                                                  Gan: "Well that's not a phone number. That's not enough numbers."                                                                                        Me: "No Gan that's the address. You said you have the phone number."

Gan: "Well I don't need the address, I need the phone number."
(Sigh.)
Me: "Okay, it starts with 706 - "
Gan: "Wait, wait a minute. You said 1305 a minute ago."
Me: "Yes Gan, but that was the address, this is the phone number."
Gan: "Well I think I have the phone number..."
At this point I collapse into uncontrollable laughter. Not the humorous kind in response to something funny, but the kind of laughter that indicates you've cracked and no longer have the ability to function.
My husband, who has been following my side of the conversation from the kitchen, watching the wrinkles on my forehead grow more prominent, graciously takes the phone from me and does his best to somehow finish the conversation. He is only on the phone 4-5 minutes, but when he gets done, tears are streaming down my face, and I'm still laughing.
It doesn't matter how prepared you think you are for her, or that you can predict her responses verbatim, frustration can't be avoided - not by any means I have yet discovered.