Interop is Hard
Simon Fell: you can read as many WS-I docs as you like, they won't tell you that you really want to avoid trying to send a nil xsd:int to .NET.
I agree with Simon, Steve, Tim, and Gia.
If you find that you must use a toolkit to help with generating the contract, I'd recommend a technique that is similar to Steve's customer's: generate WSDL using a foreign toolkit, remove all unwarranted idioms and assumptions, and then try to import the result in the toolkit that you are using to develop the service.