diff -rup drush-orig/drush.php drush/drush.php
--- drush-orig/drush.php	2009-10-26 02:26:36.000000000 +0000
+++ drush/drush.php	2009-12-30 12:10:41.000000000 +0000
@@ -5,7 +5,6 @@
  * @file
  * drush is a PHP script implementing a command line shell for Drupal.
  *
- * @requires PHP CLI 5.2.0, or newer.
  */
 
 // Terminate immediately unless invoked as a command line script
@@ -13,11 +12,7 @@ if (!drush_verify_cli()) {
   die('drush.php is designed to run via the command line.');
 }
 
-// Check supported version of PHP.
-define('DRUSH_MINIMUM_PHP', '5.2.0');
-if (version_compare(phpversion(), DRUSH_MINIMUM_PHP) < 0) {
-  die('Your command line PHP installation is too old. Drush requires at least PHP ' . DRUSH_MINIMUM_PHP . "\n");
-}
+require_once('JSON.php');
 
 define('DRUSH_BASE_PATH', dirname(__FILE__));
 define('DRUSH_COMMAND', $GLOBALS['argv'][0]);
diff -rup drush-orig/includes/backend.inc drush/includes/backend.inc
--- drush-orig/includes/backend.inc	2009-10-26 02:26:37.000000000 +0000
+++ drush/includes/backend.inc	2009-12-30 12:18:42.000000000 +0000
@@ -73,7 +73,8 @@ function drush_backend_output() {
   // Return the options that were set at the end of the process.
   $data['context']  = drush_get_merged_options();
   if (!drush_get_context('DRUSH_QUIET')) {
-    printf(DRUSH_BACKEND_OUTPUT_DELIMITER, json_encode($data));
+    $json = new Services_JSON();
+    printf(DRUSH_BACKEND_OUTPUT_DELIMITER, $json->encode($data));
   }
 }
 
@@ -102,7 +103,8 @@ function drush_backend_parse_output($str
   }
 
   if ($output) {
-    $data = json_decode($output, TRUE);
+    $json = new Services_JSON(SERVICES_JSON_LOOSE_TYPE);
+    $data = $json->decode($output);
     if (is_array($data)) {
       if ($integrate) {
         _drush_backend_integrate($data);
@@ -167,7 +169,8 @@ function _drush_proc_open($cmd, $data = 
   $process = proc_open($cmd, $descriptorspec, $pipes, null, null, array('context' => $context));
   if (is_resource($process)) {
     if ($data) {
-      fwrite($pipes[0], json_encode($data)); // pass the data array in a JSON encoded string
+      $json = new Services_JSON();
+      fwrite($pipes[0], $json->encode($data)); // pass the data array in a JSON encoded string
     }
 
     $info = stream_get_meta_data($pipes[1]);
@@ -438,7 +441,8 @@ function _drush_backend_get_stdin() {
   $string = stream_get_contents($fp);
   fclose($fp);
   if (trim($string)) {
-    return json_decode($string, TRUE);
+    $json = new Services_JSON(SERVICES_JSON_LOOSE_TYPE);
+    return $json->decode($string);
   }
   return FALSE;
 }
Only in drush: JSON.php