<p>Many products/services we are interact with (including our own) uses XML-over-HTTP or derivatives (like OMA IMPS IM/presence protocol).</p>

<p>I am looking for some tool that will "listen" to a traffic and produce client/server stubs for simulation/testing.</p>

<p>Thanks. </p>

That sounds like a good idea for a project.
This is not a solution, but your first step should be to at least support know webservice descriptors.
To do that should sniff the traffic using wireshark or something similar and see the URL's that are being accessed.  If you are lucky these services would be webservices with a retrievable descriptor or schema for the interface.  Check for .xsd, .wsdl, .asmx
Here are some examples:
http://www.webservicex.net/CurrencyConvertor.asmx
http://www.weather.gov/forecasts/xml/DWMLgen/wsdl/ndfdXML.wsdl
http://www.weather.gov/forecasts/xml/DWMLgen/schema/DWML.xsd
There are Microsoft tools available that come packaged with the SDL that can provide stubs for these.
I don't know of any drop in solution for you but my approach to solving this problem would be:
- use wireshark to record http conversations for specific webservices.
- parse (or look at) these files to extract the URLs that are invoked and track the message passing + xml documents.
- Create stubs based on what appear to be the parameters.
- Start by creating some simple pattern matchers and transforms (xml + xsl can = code or some page for debug).
You may also need to consider
- communication may not be 2 way xml- it could be HTTP posts with query string one way and xml responses back.
- The XML documents may not be properly formatted XML- test parse each message before trying to generate anything.