Stefan Priebsch has posted an example of how he uses PHPUnit "manually" to reduce the overhead (and added complexity) of calling phing.

Instead of instantiating PHPUnit from phing, I use the command line interface to call PHPUnit. This decouples phing and PHPUnit, which should cause less problems with version updates in the future. To configure PHPUnit, phing creates a temporary XML configuration file which is deleted after PHPUnit has finished.

The source is included in the post - it manually builds the XML file needed for phing to do its job.