Whenever I do WCF courses in companies that use both .NET and Java, the question of WCF interoperability always comes at some point.
My usual answer is “if you use basicHttpBinding you’ll be just fine”, which is a short answer but not a complete answer, because it doesn’t take into account things like interoperability of transport and message security (the later isn’t supported in basicHttpBinding), and the use of other WS-* standards, such as WS-ReliableMessaging, or the difference between wsHttpBinding and ws2007HttpBinding when it comes to interoperability issues. Actually even the simplest interoperability using basicHttpBinding might cause problems when the wrong data types are used on both ends.
Therefore giving such an extensive answer that covers all of those options during a course is quite problematic, so usually I give links to articles that covers some of those topics. To my delight, the WCF team has released some white papers on interoperability between WCF and other technologies, such as Java, IBM WebSphere, Oracle WebLogic and more.
In addition to those white papers here are some other links to relevant articles and blogs:
To summarize, here is the current WCF 4 WS-* interoperability matrix (taken from WCF’s MSDN website):