function chk_select(boton)
    {
        if(boton == "phone")
        {
            if(document.getElementById("callbackckbx").checked == true)
            {
                document.getElementById("callbackckbx").checked = false;
                document.getElementById("reqphonenumber").style.visibility = 'hidden';
            }
            else
            {
                document.getElementById("callbackckbx").checked = true;
                document.getElementById("reqphonenumber").style.visibility = 'visible';
            }
        } 
        if(boton == "email")
        {
            if(document.getElementById("emailckbx").checked == true)
            {
                document.getElementById("emailckbx").checked = false;
                document.getElementById("reqemailaddr").style.visibility = 'hidden';
            }
            else
            {
                document.getElementById("emailckbx").checked = true;
                document.getElementById("reqemailaddr").style.visibility = 'visible';
            }
        }
    }        

    function ValidateForm()
    {
        var firstname   = document.getElementById("firstname");
        var phonenumber = document.getElementById("phonenumber");
        var emailID     = document.getElementById("emailaddr");

        if ((firstname.value==null) || (firstname.value==""))
        {
            alert("Please Enter Your First Name");
            firstname.focus();
            return false;
        }

        if (document.getElementById("callbackckbx").checked == true)
        {
            if ((phonenumber.value==null) || (phonenumber.value==""))
            {
                alert("Please Enter a valid telephone number");
                phonenumber.focus();
                return false;
            }
        }            

        if (document.getElementById("emailckbx").checked == true)
        {
            if ((emailID.value==null) || (emailID.value==""))
            {
                alert("Please Enter a valid email");
                emailID.focus();
                return false;
            }
            if (echeck(emailID.value)==false){
                    emailID.value="";
                    emailID.focus();
                    return false;
            }

            document.frmcontact.submit()
            return true;
        }

        function echeck(str) 
        {
            var at="@";
            var dot=".";
            var lat=str.indexOf(at);
            var lstr=str.length;
            var ldot=str.indexOf(dot);
            if (str.indexOf(at)==-1){
                alert("Invalid E-mail ID");
                return false
            }

            if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){
               alert("Invalid E-mail ID");
               return false
            }

            if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){
                alert("Invalid E-mail ID");
                return false
            }

            if (str.indexOf(at,(lat+1))!=-1){
               alert("Invalid E-mail ID");
               return false
            }

            if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){
               alert("Invalid E-mail ID");
               return false
            }

            if (str.indexOf(dot,(lat+2))==-1){
               alert("Invalid E-mail ID");
               return false
            }

            if (str.indexOf(" ")!=-1){
               alert("Invalid E-mail ID");
               return false
            }

            return true					
        }
    }