The Zend Developer Zone has an announcement posted about a few new updates from Zend including i5/OS V5R3 Compatibility, a new PHP Redbook, and RPG Web Cast.
The partnership between IBM and Zend is bearing fruit once again. Not satisfied with having PHP run on IBM's i5/OS V5R4, now the two companies have put their heads together and back ported Zend Core for i5/OS to V5R3.
They've also released the redbook for it that shows you how to install, configure, and work with PHP on System i using Zend Core for i5/OS and Zend Platform for i5/OS.
As far as the webcast - you can sign up for that here and find out "Why RPG programmers should care about PHP".