If you try to make a reservation via OpenTable, most of the time tables are unavailable. When I then call the restaurant, I have never failed to get a reservation for the date and time that I am looking for. If there is a restaurant that does not accept a reservation via telephone, I simply skip it and go to another place that values their customers sufficiently to accept telephone calls. There are literally tens of top restaurants in my city, so not a problem to find one with good food AND good service (I definitely consider them accepting telephone reservations as part of good service)