onsubmit="AJAX(this);

function AJAX(pram)
        {

console.log(pram); // HtmlFormElement

            $.get("ajax.php?num="+pram, function(result){
            $("div .result").html(result);
        });
        }

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script>
$(function(){
  var selected;
  $("form.form-signin input[type='submit']").click(function(){
    selected = $(this).val();
  });
  $("form.form-signin").submit(function(){
    $.get($(this).attr("action")+"?num="+selected,function(data){
      $("div#result").html(data);
    });
    return false;
  });
});
</script>

<form class="form-signin" action="ajax.php">
  <input type="submit" name="button" value="1" />
  <input type="submit" name="button" value="2" />
  <input type="submit" name="button" value="3" />
  <br/>
  <input type="submit" name="button" value="4" />
  <input type="submit" name="button" value="5" />
  <input type="submit" name="button" value="6" />
  <br/>
  <input type="submit" name="button" value="7" />
  <input type="submit" name="button" value="8" />
  <input type="submit" name="button" value="9" />
  <br/>
  <input type="submit" name="button" value="*" />
  <input type="submit" name="button" value="0" />
  <input type="submit" name="button" value="#" />
</form>

<div id="result"></div>