phone not availabe

[whydidibuypontiac]

Hello everyone . I am posting for my mothers van if that helps! lol

My mothers 2005 Montana is possesed and the question is about the woman continously telling her "phone not available". Ive been searching for awhile now and other GM vehicles have the same problem, but apparently her Montana is the only one its happened to. The dealer had just given her the run around telling us it was ONSTAR and when I talked to ONSTAR they said to take it to the dealer. Now the dealer is closed so no more asking them for help.
So the questions are how to disable the ONSTAR.
#1- Ive tried to remove the fuse but it didnt seem to do anything.Was it the wrong fuse ?
#2- Can I unplug the ONSTAR box? If I can, where would it be?
#3- Is there ANYTHING I can do for her.
She makes her living driving and is in her van ALL DAY!
So if anyone can help me or push in the right direction , I would be very, very thankful.
If this has happened to you, i'd love to hear how you resolved it.
Thanks again for reading and stay cool.