<input type="tel" placeholder="+7-xxx-xxx-xx-xx" id="sipphone"/>
<a href="#" class="callbtn">Позвонить</a>

.callbtn {
  display: block;
  width: 100px;
  text-align: center;
  margin-top: 10px;
  padding: 5px 10px;
  background: #eee;
  border: 2px solid #484848;
  text-decoration: none;
  color: #484848;
}
.callbtn:hover {
  background: #484848;
  color: #fff;
  transition: 0.5s all ease;
}

$("#sipphone").mask("+79999999999");

$(document).ready(function() {
    $('#sipphone').change(function() {
      var newurl = $('#sipphone').val();
      $('a.callbtn').attr('href', "call:" + newurl);
      $('a.callbtn').html("Позвонить<br>" + newurl)
    });
});