Ariz Jacinto has written up a new post with the commands you'll need to get PHP up and runnign with MSSQL Server's native ODBC driver working on linux (accessible through PDO).
Last month, MS announced the preview release of SQL Server ODBC Driver for Linux, a 64-bit binary driver for Red Hat Enterprise Linux 5. This is good news for companies using heterogenous platforms e.g. LAMP stack running a PHP application that connects to both MySQL and MSSQL Server. Meaning, these companies no longer have to use third-party drivers such as FreeTDS that MS doesn't support. Then a few days ago, MS released version 1 of the driver. I immediately downloaded the driver and recompiled PHP with it as a PDO (PHP Data Object) ODBC driver.
His process has five steps to it, including one for making a test script (code included) and another with a few gotchas/performance considerations to keep an eye out for when using the driver.