<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<div class="container">
<div class="row">
<a href="tel:1234123412" class="btn btn-primary btn-lg" title="Call Us" id="call-us" rel="external">Call Us</a>
<div class="locations-container" style="position:absolute;top:0;opacity:0;">
<select class="form-control" id="location-select">
<option value="">Select Location</option>
<option value="tel:1234123412">Nebraska</option>
<option value="tel:12341234">California</option>
<option value="tel:12341234">Iowa</option>
</select>
</div>
</div>
</div>