SO custom mobile breaks

HTML

<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/css/bootstrap-combined.min.css">
<script src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/js/bootstrap.min.js"></script>
<div class="container">
  <div class="row-fluid phone-two">
    <div class="span3">
      phone-two span3
    </div>
    <div class="span3">
      phone-two span3
    </div>
      <div class="span3">
      phone-two span3
    </div>
      <div class="span3">
      phone-two span3
    </div>
  </div>
    
    <div class="row-fluid">
    <div class="span3">
      std span3
    </div>
    <div class="span3">
      std span3
    </div><div class="span3">
      std span3
    </div>
        <div class="span3">
      std span3
    </div>
  </div>
    
</div>

CSS

.span3{
 background-color:#ddd;
 border-bottom:2px solid white;
}
@media (max-width: 767px) {
.row-fluid.phone-two .span3 {
    width: 48%;
    margin-left: 4%;
    float:left;
}
.row-fluid.phone-two > .span3:nth-child(odd){
    margin-left: 0;
}
}