A simple way to turn-on SOAP message logging is to add something like the below to app.config

<system.diagnostics>
<sources>
<source name="System.ServiceModel.MessageLogging">
<listeners>
<add name="messages"
type="System.Diagnostics.XmlWriterTraceListener"
initializeData="c:\logs\messages.svclog" />
</listeners>
</source>
</sources>
</system.diagnostics>

<system.serviceModel>
<diagnostics>
<messageLogging
logEntireMessage="true"
logMalformedMessages="false"
logMessagesAtServiceLevel="true"
logMessagesAtTransportLevel="false"
maxMessagesToLog="3000"
maxSizeOfMessageToLog="2000"/>
</diagnostics>
</system.serviceModel>