Page 1085 of the 1240 page Application Development manual discusses configuring data services.
AMFPHP is a clone of Flash Remoting. Flash Remoting is not the same as FDS, and FDS is not a drop-in replacement.
In short, Flash Remoting only manages function calls to various server-side programs, and you do the rest. FDS does not support certain Flash Remoting functionality, but provides many other features which are way beyond the scope of Flash Remoting such as RTMP, publish/subscribe messaging, conflict resolution, data replication, and occasionally connected clients.
Which is a section titled "Flex Data Services configuration", and most of the subsections are blank. (at the time of this writing.)
And, about FDS v remoting- what I have right now is actionscript 2 talking to PHP via AMFPHP. So,
If I wanted to switch to Flex and FDS, would I necessarily have to stop using PHP?
Are the features of FDS a superset of the features of remoting? Would one typically use both remoting and FDS together, or does FDS do everything that remoting can do, plus more, hence remoting goes away?
If you're using Flex Builder you have to point the project at your /WEB-INF/flex/flex-enterprise-services.xml configuration file. Depending on how you set up the project, you may specify this as a compiler argumetn using --services=c:/dev/yourappserver/flex/WEB-INF/flex/flex-enterprise-services.xml
Same command line argument goes if compiling with mxmlc.exe directly.