Hi,
Did you manage to go farther in your research about creating a client for Exchange 2K7 using JAVA ?
I can give you a feed back about it, even if I did not succeed yet to use the interface provided in the wsdl file. I generated the java package using axis, and it worked fine, even if I had to correct a number of constructor in classes in order to propagate the correct inheritance. It seems that axis2 report a problem when generating the package, because the service tag is missing. Any way, using axis, you can get a package that works. The problem is that the generated interface does not really correspond to the one generated on .Net. It seems that every request required the following objects: ExchangeImpersonationTYpe & SerialiezdSecurityContextType. These are properties of the class ExchangeServiceBinding, but I don't know yet how to initialize them correctly.
Hope this information may help you. And If you have any feed back about what you tried...