I am not sure how you would even file charges.  I would guess that you would have to contact the prosecutor's office and convince them to bring charges.  Most likely they would consider non-payment by a client to be a civil matter and they will tell you to sue them.  It seems like a long shot to me, but I'm not familiar with the laws in Pennsylvania.

Depending on the amount in controversy, it can usually be done via private criminal complaint at the District Justice (Magistrate) level.  I saw one such case of Theft by Deception filed in Blair county by a client who alleged that his attorney engaged in a course of conduct which resulted in the complainant being defrauded of monies paid to the attorney as a retainer.  Even so, the complaint would have to be submitted to the DA for approval.

Regards,
Scott Perry