Digital radio emerged in the radio market backed by large corporations such as Viacom, ClearChannel, Entercom, and Cox Radio in response to the successful emersion of satellite radio corporations XM and Sirius. When satellite radio emerged on the scene, terrestrial radio corporations were already planning a swing back to limit users from leaving conventional radio but never planned for the explosion of popularity that satellite radio would receive.
Mostly, they hedged their bets on the fact that many radio listeners would balk at shelling out money for new equipment as well as paying for a monthly subscription service but as it turns out, the marketing campaigns of both XM and Sirius have done their job well. To help integrate satellite radio into terrestrial radio's listener base, satellite radio companies enlisted the help of major automobile manufacturers such as GM to include the equipment into their new vehicles and offered the first several months' service for free, effectively allowing users to try before they buy.
But digital radio has seen a growing amount of popularity as well. Often touted as "HD-Radio" which capitalizes on the immense popularity of high definition capable televisions, digital radio utilizes offset frequencies on the traditional dial to broadcast their digital signals much like terrestrial radio. Additionally, digital radio will remain "free" to radio listeners but they still will have to shell out the money for special integration equipment for the home and automobile. However, like satellite radio has done in the past, many digital radio proponents are sealing deals where they know the majority of their marketplace listens to the radio - in their cars.