This is working code.
function validateSignup()
{   
    $.validator.addMethod(
            "regex",
            function(value, element, regexp) 
            {
                if (regexp.constructor != RegExp)
                    regexp = new RegExp(regexp);
                else if (regexp.global)
                    regexp.lastIndex = 0;
                return this.optional(element) || regexp.test(value);
            },
            "Please check your input."
    );
    $('#signupForm').validate(
    {
        onkeyup : false,
        errorClass: "req_mess",
        ignore: ":hidden",
        validClass: "signup_valid_class",
        errorClass: "signup_error_class",
        rules:
        {
            email:
            {
                required: true,
                email: true,
                regex: /^[A-Za-z0-9_]+\@[A-Za-z0-9_]+\.[A-Za-z0-9_]+/,
            },
            userId:
            {
                required: true,
                minlength: 6,
                maxlength: 15,
                regex: /^[A-Za-z0-9_]{6,15}$/,
            },
            phoneNum:
            {
                required: true,
                regex: /^[+-]{1}[0-9]{1,3}\-[0-9]{10}$/,
            },
        },
        messages: 
        {
            email: 
            {
                required: 'You must enter a email',
                regex: 'Please enter a valid email without spacial chars, ie, Example@gmail.com'
            },
            userId:
            {
                required: 'Alphanumeric, _, min:6, max:15',
                regex: "Please enter any alphaNumeric char of length between 6-15, ie, sbp_arun_2016"
            },
            phoneNum: 
            {
                required: "Please enter your phone number",
                regex: "e.g. +91-1234567890"    
            },
        },
        submitHandler: function (form)
        {
            return true;
        }
    });
}