All of the reples make no sense whatsover to me.
The original poster makes a very clear question that how to send attachments using soap way that works with many environments. For example, Axis and .Net.
To rephrase this, I would say how to create a Wsdl that works with both axis and .net. Currently, using the DataHandler in the wsdl (or generating the wsdl from java code with DataHandler) would not work with other environment. I haven't tried this, but looking at the definition of DataHandler (package name), and its namespace in the wsdl, you can tell it comes from apache, not some Soap standard, unless Apache is the official standard used for attachment.
It's funny to read a bunch of replies that have little answer value to the original question.
