I've written a new IL for jbossmq that encodes all messages in xml. Right now, the IL is structured like UIL, using a single multiplexed server socket.
In addition to the java xil package, I have started a C# jms client package. Since the xil sends all messages using primary data types as specified by the DataInput/OutputStream classes in jdk1.4.1 (bytes, ints, longs, and UTF8 chars), a client library could be implemented in any language. Our current project is a C# application, so we have started there. The C# lib could be used from VB, J#, or Managed C/C++.
However, anyone interested could implement a client in any language.
Right now, the xil can send text and bytes messages.
Please check out the csil project on sourceforge: csil.sourceforge.net.