Of course, because Ms. Palfrey's clients included prominent business and government figures --- among them former Bill Clinton svengali Dick Morris and recently resigned State Dept foreign aid adviser Randall Tobias, according to the NY Times --- one strongly suspects that she wants to call these witnesses less to exonerate herself but in the hope that the powerful clients, fearing exposure, will use their influence to get the charges dropped. (But I'm betting that firing the responsible Justice Dept lawyers isn't exactly an option right now.)
This is a truly elegant legal strategy because the former clients' testimony is undoubtedly relevant and not merely cumulative of what the escorts themselves could say if called to testify. Although the escorts and the clients both have an incentive to claim (whether truthfully or falsely) that there was no sex for money, Palfrey can plausibly argue that she needs the client testimony because she shouldn't be forced to make her defense turn on the credibility of alleged call girls, when she can call pillars of the community. And of course, even a former client who would say that he was only paying for massages or other legal services, will be terrified of the adverse publicity. This defense is tailor-made for tv drama.