Tony,
I assume you mean a TOC (like ArcMap) that has layer symbology. WMS is a very different creature than a ArcGIS Server Map Service and thus the access to the legend may of may not exist on the WMS server, this make it difficult to work with WMS. There is not a solution out there that I am aware of.
As you can see from this ArcGIS Bug, even ArcMap can have issues:
http://support.esri.com/en/knowledgebase/techarticles/detail/27951