Harvard's Center for Hellenic Studies has recently published online A. Cameron's volume on Dialoguing in Late Antiquity.
A passage from the Introduction:
This book is about a particular form of writing by Christians in late antiquity, sometimes referred to as “the philosophical dialogue”—although by no means all the dialogues in question can be regarded as philosophical. The subject is central to the much wider question of the development of a specifically Christian rhetoric, especially in Perelman’s sense in which “the realm of rhetoric” constitutes “the entire universe of argumentative discourse,”  for Christian writers did indeed use the dialogue form as part of their argumentative endeavor.
Click here to read the book