I generally am in the camp of regarding the phone call as being an acceptable price to pay for the convenience of making a reservation. However, earlier this year I was having a frantic day and I came out of a meeting with nine voicemails requiring attention and no time to deal with them. Because the restaurant was just a phone number and not a name, I didn't get round to it and they cancelled the reservation.
I prefer restaurants which send a text asking to respond Y or N. It seems so much faster, easier and more efficient.