diff --git a/gen_pc_sidecar.php b/gen_pc_sidecar.php
index 20c6e64..97983c4 100755
--- a/gen_pc_sidecar.php
+++ b/gen_pc_sidecar.php
@@ -18,7 +18,12 @@ function main(): void {
   $argv = $_SERVER['argv'] ?? [];
   $do_notify = in_array('--notify', $argv, true);
 
-  $pbdb = trim_db(pull_db());
+  $pbdb = pull_db();
+
+  prepend_contact_list($pbdb);
+  blacklist_terms($pbdb);
+  filter_extensions($pbdb);
+
 
   $mac_list = pull_mac_list();
 
@@ -68,9 +73,75 @@ function pull_db(): array {
     return $pbdb;
   }
 
-function trim_db($pbdb): array {
-  global $BLACKLISTED_TERMS;
+function filter_extensions(&$pbdb) {
+  global $LIST_FILTER_TYPE;
 
+  if ($LIST_FILTER_TYPE == "whitelist") {
+    whitelist_extension_filter($pbdb);
+  } elseif ($LIST_FILTER_TYPE == "blacklist") {
+    blacklist_extension_filter($pbdb);
+  } else {
+    fwrite(STDERR, "Filter type invalid: $LIST_FILTER_TYPE");
+    fwrite(STDERR, "Use either whitelist or blacklist");
+  }
+}
+
+function blacklist_terms(&$pbdb) {
+  global $BLACKLISTED_TERMS;
+  
+  $pbdb = array_values(array_filter($pbdb, function ($item) use ($BLACKLISTED_TERMS) {
+      if (!is_array($item) || !isset($item['name'])) {
+          return true;
+      }
+
+      $name = ltrim($item['name']);
+
+      foreach ($BLACKLISTED_TERMS as $term) {
+          if (stripos($name, $term) === 0) {
+              return false;
+          }
+      }
+      return true;
+  }));
+}
+
+function whitelist_extension_filter(&$pbdb) {
+  global $EXTENSION_FILTER_LIST;
+   
+  $allowed = array_fill_keys(
+      array_map('trim', array_map('strval', $EXTENSION_FILTER_LIST)),
+      true
+  );
+
+  $pbdb = array_values(array_filter($pbdb, function ($item) use ($allowed) {
+      if (!is_array($item) || !isset($item['extension'])) {
+          return false;
+      }
+
+      $ext = trim((string)$item['extension']);
+      return isset($allowed[$ext]);
+  }));
+}
+
+function blacklist_extension_filter(&$pbdb) {
+  global $EXTENSION_FILTER_LIST;
+
+  $blocked = array_fill_keys(
+      array_map('trim', array_map('strval', $EXTENSION_FILTER_LIST)),
+      true
+  );
+
+  $pbdb = array_values(array_filter($pbdb, function ($item) use ($blocked) {
+      if (!is_array($item) || !isset($item['extension'])) {
+          return true;
+      }
+
+      $ext = trim((string)$item['extension']);
+      return !isset($blocked[$ext]);
+  }));
+}
+
+function prepend_contact_list(&$pbdb) {
   $pbdb_prepend = [
     [ 'name' => 'Night Hours', 'extension' => '*271', ],
     [ 'name' => 'Overhead Page', 'extension' => '900', ],
@@ -80,22 +151,6 @@ function trim_db($pbdb): array {
   ];
 
   array_unshift($pbdb, ...$pbdb_prepend);
-  
-  $filtered = array_filter($pbdb, function ($item) use ($BLACKLISTED_TERMS) {
-      if (!is_array($item) || !isset($item['name'])) {
-          return true;
-      }
-      $name = ltrim($item['name']);
-
-      foreach ($BLACKLISTED_TERMS as $BLACKLISTED_TERM) {
-          if (stripos($name, $BLACKLISTED_TERM) === 0) {
-              return false;
-          }
-      }
-      return true;
-  });
-
-  return $filtered;
 }
 
 function pull_mac_list(): array {
@@ -120,6 +175,13 @@ function read_config_ini($CONFIG_KEY): array {
   $config = parse_ini_file('config.ini');
   $config_value = preg_split('/\s*,\s*/', $config[$CONFIG_KEY] ?? '', -1, PREG_SPLIT_NO_EMPTY);
 
+  $config_value = array_map(
+      fn($v) => strtolower(trim((string)$v)),
+      $config_value
+  );
+
+  $config_value = array_values(array_filter($config_value, fn($v) => $v !== ''));
+
   return $config_value;
 }
 
@@ -183,12 +245,12 @@ function write_attendants($attendant, $pbdb): void {
   $index =  1;
   foreach ($pbdb as $r) {
       $label = trim((string)($r['name'] ?? ''));
-      $address  = trim((string)($r['extension'] ?? ''));
+      $address = trim((string)($r['extension'] ?? ''));
       $type = trim((string)("normal"));
 
       $attendant->setAttribute("attendant.resourceList.{$index}.address", $address);
-      $attendant->setAttribute("attendant.resourceList.{$index}.label",   $label);
-      $attendant->setAttribute("attendant.resourceList.{$index}.type",    $type);
+      $attendant->setAttribute("attendant.resourceList.{$index}.label", $label);
+      $attendant->setAttribute("attendant.resourceList.{$index}.type", $type);
 
       $index++;
   }