Something

if ($act == "save"){
$a =$_POST['CustomerID'];
$b =$_POST['Company'];
$c =$_POST['Contact'];
$d =$_POST['LastName'];
$e =$_POST['Address'];
$f =$_POST['City'];
$g =$_POST['State'];
$h =$_POST['Country'];
$i =$_POST['ZipCode'];
$j =$_POST['Phone'];
$k =$_POST['Fax'];
$l =$_POST['Interests'];
$m =$_POST['ResellNumber'];
$n =$_POST['Wanted'];
$o=$_POST['User1'];
$p =$_POST['User2'];
$q =$_POST['User3'];
$r =$_POST['User4'];
$s =$_POST['User5'];
if ($b==null &&
$c==null &&
$d==null &&
$e==null &&
$f==null &&
$g==null &&
$h==null &&
$j==null &&
$k==null &&
$l==null &&
$m==null &&
$n==null &&
$o==null &&
$p==null &&
$q==null &&
$r==null &&
$s==null){
echo "$f,Please fill in at least one of the fields!";
}else 
{