My daughter has a list of where she will not answer or call on her phone.
In her car while driving (It could cost her, her job if she is stopped for using her cell phone while driving.)
At work
In a restaurant
At home after 9 p.m.
In a hospital
And when visiting someone in their home.
She got so sick of her daughter calling her at the most inopportune times, for the most stupid reasons, that she had to set rules. We liked the idea, so we all agreed to practice them ourselves. Except for me, talking to long distance friends.
Don't bother to try and call her during these times. She won't respond. If you know her, then you know the rules. So you don't call. When she has a chance, she will peek at who called. Then return the call at her convenience. If she doesn't know you, you may never hear from her.
On the other hand, my youngest is in medicine. He works in the ER. He answers his phone for every medical call. Also all his emails go to his phone and alerts him. I am quite often awake late into the evening when I know he is sleeping. I will send him an email. I have told him to never answer my call immediately. In fact, sometimes I get no response to my email. Since he is my medical proxy he knows I am not in any danger and if I was the hospital would be calling him, not me.
I resisted for a long time before I decided to get a cell phone. And then it was only to cut my phone bill down. I opted for the free one. I get 250 minutes a month with 250 something for texting. I have yet to text anyone in my life. Most of my minutes and all of my text things go back unused. This whole family knows what the rules are between us. We don't break them because we know we won't get a response.