How to intercept raw soap request/response (data) from WCF client

You don't have a specific tab that shows just the SOAP message - but the XML tab does include the whole SOAP message - no??

What is missing for you from this snippet of XML here??

UPDATE: John, you're unfortunately not showing what your <system.serviceModel>/<diagnostics> section looks like - mine used for this result looks like this:

<diagnostics>
  <messageLogging 
      logMessagesAtTransportLevel="true" 
      logMessagesAtServiceLevel="false"
      logMalformedMessages="true" 
      logEntireMessage="true"
      maxSizeOfMessageToLog="65535000" 
      maxMessagesToLog="500" />
</diagnostics>

Do you have the same settings? Maybe you're missing logEntireMessage or something else??

I recently encountered the same problem as in the update to the original question: the trace was showing that a message had been sent, but the message itself wasn't there. For me, the fix was to add a System.ServiceModel.MessageLogging source. Here's my system.diagnostics config section:

<system.diagnostics>
   <sources>
      <source name="System.ServiceModel" 
              switchValue="Information, ActivityTracing" 
              propagateActivity="true" >
         <listeners>
            <add name="xml"/>
         </listeners>
      </source>
      <source name="System.ServiceModel.MessageLogging">
         <listeners>
            <add name="xml"/>
         </listeners>
      </source>
   </sources>
   <sharedListeners>
      <add name="xml" 
           type="System.Diagnostics.XmlWriterTraceListener" 
           initializeData="C:\logfiles\Traces.svclog" />
   </sharedListeners>
</system.diagnostics>

And my system.serviceModel / diagnostics section:

<diagnostics>
   <messageLogging
      logMessagesAtTransportLevel="true"
      logMessagesAtServiceLevel="true"
      logMalformedMessages="true"
      logEntireMessage="true"
      maxSizeOfMessageToLog="65535000"
      maxMessagesToLog="500" />
</diagnostics>

Once I added the MessageLogging source, the TraceViewer showed "Message Log Trace" traces which contained the actual SOAP messages.