How to discover custom field meta-data

Using SuiteTalk, what's the preferred way for me to get custom data for a given entity? 

This is for an integration effort, so we cannot assume that any of the UI is available, or that my code will have any information beyond what can be gotten from the WSDL.

To keep it simple, let's say it's a contact, who has one custom field defined.  I'm getting the contact back as a result from an advanced customer search to which I have done a contactJoin.  I see that I can get back a customFieldList as part of that join.

But at that point, things become fuzzy.  I followed it through the xsd, and it seems that I will need the internal ID in order to get the value of the custom field?  But I don't have the internal ID.  (Am I looking at the wrong structure?)