SAN FRANCISCO — Say you are in a strange city and need a hotel for the night. You pull out your phone, search for hotels on Google and see a nearby one listed at the top of the rankings, with a little phone icon that says, ‘‘Call.’’ You tap it, reach the hotel, and ask for a room.

And just like that, Google made money. That icon was a so-called click-to-call ad, and the hotel paid Google for it when you called.