In this recent article from the Zend Developer Zone Jack Herrington takes a look at the component of the Zend Framework that lets it talk directly to Flash and Flex applications - Zend_Amf.
Reading and posting to Extensible Markup Language (XML)–based services with Adobe Flex is easy. But what’s even easier is using Adobe’s Action Message Format (AMF) to send messages between the Flex client and the server. It’s as easy to use as a method call on an object. This article shows how to set up an AMF service [so you can use this method] on your PHP web server using the Zend Framework and Zend_Amf.
As his example application, he sets up a contacts database he'll pull information from and insert data into from his Flex form. You'll need to already be familiar with working in a Zend Framework instance before you get started - he dives right into the code. Screenshots and code for both the PHP and Flex sides of things are included