[This forum posting] includes source to access D3 from PHP using FlashCONNECT?. However the server can be any process that returns a delimited string, the connectivity can be any valid pipe. So you can use the same technique to access jBase with REST, U2 with a WebService? and UniObjects? ... any technology of your choice.
Accessing U2 from PHP is U2-specific, but as with the above the same techniques, and code to a great extent, can be used with any MV environment.
Web Application Server: PHP to D3 : http://www.pfinders.com/phptod3/