function submit_form()
{ 
  if (document.forms.contactus.phone.value != "")
    document.forms.contactus.submit();
  else
  {
    if (document.forms.contactus.email.value.indexOf("@") == -1)
     email_fail ("No '@' in address, please re-enter");
    else
    {
       var emailadr = document.forms.contactus.email.value.split("@");
       if (emailadr[1].length < 3) email_fail ("Domain name incorrect, please re-enter");
       else if (emailadr[1].indexOf(".") == -1) email_fail ("No dot in address, please re-enter");
       else 
        document.forms.contactus.submit();
     }
   }
}
function email_fail(errmsg)
{ 
 alert ("Email address error:\n" + errmsg);
}