function verifyone() {
var themessage = "You are required to complete the following fields: ";

if (document.callbackform.name.value=="") {
themessage = themessage + "name, ";
}
if (document.callbackform.tel.value=="") {
themessage = themessage + "tel, ";
}
//alert if fields are empty and cancel form submit
if (themessage == "You are required to complete the following fields: ") {
document.callbackform.submit();
}
else {
alert(themessage);
return false;
   }
}