Daniel Krook has written up an entry talking about the collaboration that Zend and IBM have created in the form of PHP for i5/OS.

OK, I'll be the first to admit that I'm not all that familiar with the nuances of IBM's server brands, despite working for Big Blue. [...] If you *do* happen to have an IBM System i machine, you might be interested in some of the following new developments:

The two items he points to are the latest Zend Core for IBM that's been released and a new Redbook IBM has published to accompany PHP's introduction to IBM's world and to help you get it installed.