jQuery validate with AJAX

HTML

<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.9/jquery.validate.js"></script>
<script src="http://ajax.cdnjs.com/ajax/libs/json2/20110223/json2.js"></script>
<form>
<input type="tel" name="mobilenumber" />
<input type="submit" />
</form>

CSS

.error{
    color: Red;
}

JavaScript

// regex validator
$.validator.addMethod(
        "regex",
        function(value, element, regexp) {
            var re = new RegExp(regexp);
            return this.optional(element) || re.test(value);
        },
        "Please check your input (Regex)"
);

// custom validator method for jQuery validator
// will return valid result for 0411112222
$.validator.addMethod("vnumber", function (value, element, params) {
    var isValid = false;
    var u = "http://110.142.96.71/Splendour/Virgin/IsVirginNumber?mobile=" + value;
    alert(u);
    $.ajax({ 
        url: u, 
        type: "GET",
        async:false,
        //data: { 
        //    number: value, 
            
            // configure AJAX response using JsFiddle echo
            //delay: .5,
            //json: JSON.stringify({ isValid: value == "0411112222" })          
        //},
        
        success: function(response) { 
            alert('Hi');
            //if (response.isValidVirginNumber == "true")
            //    isValid = true;
        }
      });
    return isValid;
    
}, "Not a Virgin Number");


$("form").submit(function(e) {
    e.preventDefault();
    
    // validation rules
    $("form").validate({ rules: {
        mobilenumber: { 
            number: true, 
            regex: "^04[0-9]{8}",
            vnumber: { message: "123" }}
    } });
    
    if($("form").valid())
    {
        alert("This is a valid number!");
    }
});

// show qr code for current page URL
$(document).ready(function() {
    $("body").append($("<img />").attr("src", "http://chart.apis.google.com/chart?cht=qr&chs=150x150&chl=" + encodeURIComponent(window.location)));
});