What's your opinion on cell phone usage in restaurants?

The other day my stepmom started a phone conversation with her friend 2 hours before we left for dinner. The conversation continued for 20 minutes in the car ride to the restaurant (upon arrival at the restaurant she complained because it wasn’t where she wanted to go). Then it continued as we were led to our seats and when the waiter arrived to take our drink orders.
He said he would return when she was done talking and he did.
But as he came back, my father answered a phone call from my brother and ignored the waiter by talking over him.
And the rest of dinner my stepmom was on her phone texting her friend.

I was thoroughly embarrassed and this isn’t even the first time.
We’ve been out to dinner before where she was on her phone talking to her friend the entire time and even after we left. Me and my dad just sat in silence so as not to interrupt her conversation.

So, what’s your opinion on cell phone usage in a restaurant?

I find it very rude and feel particularly bad for the waiters because I’m not sure how I would handle someone who would rather be on their phone than order food.