If you need to log SOAP information in Websphere, you can turn on trace logging and set the following value in the Change Log Details Level (Logging and Tracing > ServerName > Diagnostic Trace Service > Change Log Detail Levels) :

com.ibm.ws.webservices.engine.*=all

This will log only the SOAP web service messages without seeing all of the other goop that can make the trace log hard to read through.

Make sure you have a valid trace log file defined first (${LOG_ROOT}/trace.log)