In the early years of radio, people used the radio as a way to communicate to the community about varying concerns as well as sharing the airwaves with NBC programming. This then changed when the RCA offered Class A and Class B licenses to decide who could be on the air. This took away o a lot of individuals opportunity to use the radio. But as the NBC grew, more stations were created, and in turn those stations also made sure to focus on local needs as well as playing network programming as well. The strategy overall is to slowly let the larger commercial organizations cover more and more area, and while this got rid of citizen's radio, NBC tried to compensate by having their stations have a local focus.
The popularity with radios began due to local enthusiasm and it seems that the networks made sure to preserve its public service obligation because of this fact. By allowing the local stations determine programming, networks gave them the power and creativity to follow their public service obligations. Though it seems that as time went on the commercial mandate took over as networks pushed for network programming over local.