<style type="text/css">
  .mobileShow {display: none;}

  /* Smartphone Portrait and Landscape */
  @media only screen
    and (min-device-width : 320px)
    and (max-device-width : 480px){
      .mobileShow {display: inline;}
  }
</style>

<div class="mobileShow">
reklam kodu buraya
</div>