On the Dev-Explorer blog there's a post made recently about using stored procedures in your MySQL database via the mysqli interface in PHP.
On a new project I am working on I decided to take a look at the MySQLi (MySQL Improved) library. Most of the functions remain the same but it can now be used in object orientated programming which seemed to me as big advantage. Below I look at implementing MySQLi and extending it with your own custom code, along with using it to execute stored procedures.
He shows how to create both pieces of the puzzle - the class extending the mysqli functionality and a simple stored procedure on the database side (to insert users into a table). They're tied together with a PHP class with a "storedProcedure" method that runs a query() with a "CALL" to the procedure name.