pɹˈaɪɚ tə ðə dʒˈænjuːˌɛɹi nˈaɪntiːnhˈʌndɹɪd twˈɛnti θɹˈiː ɪstˈæblɪʃmənt ʌvðə mˌɪsɪsˈɪpi ɹˈɪvɚɹ æz ðə bˈaʊndɚɹi, kˈɔːl lˈɛɾɚz bɪɡˈɪnɪŋ wɪð "dˈʌbəljˌuː" wɜː dʒˈɛnɚɹəli ɐsˈaɪnd tə stˈeɪʃənz ˈiːst əvən ɪɹˈɛɡjʊlɚ lˈaɪn fˈɔːɹmd baɪ ðə wˈɛstɚn stˈeɪt bˈoːɹdɚz fɹʌm nˈɔːɹθ dɐkˈoʊɾə sˈaʊθ tə tˈɛksəs, wɪð kˈɔːlz bɪɡˈɪnɪŋ wɪð "kˈeɪ" ɡˌoʊɪŋ ˈoʊnli tə stˈeɪʃənz ɪn stˈeɪts wˈɛst ʌv ðæt lˈaɪn.
Prior to the January 1923 establishment of the Mississippi River as the boundary, call letters beginning with "W" were generally assigned to stations east of an irregular line formed by the western state borders from North Dakota south to Texas, with calls beginning with "K" going only to stations in states west of that line.