http://www.wlshistory.com/
The early 1920's. Birth of commercial radio as we know it today. In the Midwest, Sears-Roebuck and Company had flirted with the new medium by buying time on radio stations to address and target the lucrative farming market. By 1923, it was apparent to Sears that they needed their own broadcast outlet to continue their relationship with the farmers. As a result, the company started the Sears-Roebuck Agricultural Foundation, designed to be a clearinghouse for information and assistance through its Farm and Home Service Departments. In order to carry out the foundation, Sears originally did a farm program beginning on March 21, 1924, with its first assigned call letters WBBX, from the studios of WMAQ Radio.
WLS really reached a lot of territory.