1. A directory assistance service system comprising: a memory that stores instructions; a processor that executes the instructions to perform operations, the operations comprising: storing a set of audio advertisements priced on a tiered pricing model, wherein the set of audio advertisements are placed in different tiers based on a size of an advertiser associated with a particular advertisement, a type of business of the advertiser, and a number of locations of the advertiser; and receiving a directory assistance request from a caller; selecting an audio advertisement from the set of audio advertisements; playing, to the caller, the audio advertisement that is selected from the set of audio advertisements and charging, based on the tiered pricing model, the advertiser for playing the audio advertisement that is selected from the set of audio advertisements, wherein the set of audio advertisements is rotated for selection, and wherein the audio advertisement that is selected from the set of audio advertisements is rotated more frequently in response to the advertiser paying more for the audio advertisement that is selected from the set of audio advertisements.