Hi, we tried the following example :
<?php
  $proc_qry = "CALL CM.CLIBROS(? , ? , ?)";
  $dbconn = dbconnect();
  $proc_stmt = odbc_prepare($dbconn,$proc_qry);
  $codFon = 0;
  $codPYC = "010";
  $codRet = "";
  $values = array ($codFon,$codPYC,$codRet);
  $result = odbc_execute($proc_stmt,$values) ;
  while(odbc_fetch_row($result)){
    for($i=1;$i<=odbc_num_fields($result);$i++){
       echo "colonne ".i." : ".odbc_result($result,$i);
    } //for
  } //while

the third parameter of CLIBROS stored procedure is an output parameter. PHP reported this error :
 [error] PHP Warning:  odbc_execute(): SQL error: [IBM][CLI Driver] CLI0005W  Option value changed. SQLSTATE=01S02, SQL state 01S02 in SQLExecute in testPRS.php on line 31

we didn't find how to register an output parameter for the statement.

There are now a number of native drivers that explicitly support OUT parameters from stored procedures; for your particular example, the ibm_db2 extension in PECL (http://pecl.php.net/ibm_db2, with docs available at http://php.net/ibm_db2) supports OUT parameters for DB2, Cloudscape, and Apache Derby databases beginning with PHP 4.3.11 and higher (including PHP 5.0/5.1).

Apparently the challenge with making this support available in the Unified ODBC extension is that the specific requirements vary so much by database that it is next to impossible to extend support for every feature for every database in the Unified ODBC extension -- therefore, the mssql extension supports OUT parms for MS SQL Server, the OCI8 extension supports OUT parms for Oracle, the ibm_db2 extension supports OUT parms for DB2, etc. 

Note that the PDO_ODBC driver for the PHP Data Objects (PDO) extension does support OUT parms for DB2 natively, as well as other databases that offer ODBC drivers. PDO requires PHP 5.0 and above.

So I'm closing this as "Won't fix", noting that there are better alternatives than the Unified ODBC extension for this functionality.