OpenTable has the advantage too of already having lots of their customers' phone numbers on file, which opens the door to some interesting matching/analytics opportunities.
Restaurant A might want to know, for example, that many of the same customers who walk in to their restaurant make reservations at B & C instead -- perhaps A might want to make changes so that people plan ahead to eat there rather than just walk in.
a) Sit at the bar and order a drink b) Sit in the waiting area and read posters/chalkboards about upcoming events, happy hour specials, gift certificates/loyalty programs, etc.
Either way, the restaurant comes out ahead (especially at the bar, where alcoholic beverage margins make every restaurant owner smile). I wouldn't be surprised if a restaurant saw a decrease in drinks purchased if customers were allowed to freely wander beyond the range of those pager devices.