$.validator.addMethod("phone", function(phone_number, element) {
    var digits = "0123456789";
    var phoneNumberDelimiters = "()- ext.";
    var validWorldPhoneChars = phoneNumberDelimiters + "+";
    var minDigitsInIPhoneNumber = 10;
    s = stripCharsInBag(phone_number, validWorldPhoneChars);
    return this.optional(element) || isInteger(s) && s.length >= minDigitsInIPhoneNumber;
}, "Please enter a valid phone number");

function isInteger(s) {
    var i;
    for (i = 0; i < s.length; i++) {
        // Check that current character is number.
        var c = s.charAt(i);
        if (((c < "0") || (c > "9"))) return false;
    }
    // All characters are numbers.
    return true;
}
function stripCharsInBag(s, bag) {
    var i;
    var returnString = "";
    // Search through string's characters one by one.
    // If character is not in bag, append to returnString.
    for (i = 0; i < s.length; i++) {
        // Check that current character isn't whitespace.
        var c = s.charAt(i);
        if (bag.indexOf(c) == -1) returnString += c;
    }
    return returnString;
}