Does WebSphere have support for MTOM and XOP?
Back in Feb. 2005, I talked about new specs from the W3C to make XML more efficient (Better Web Services Performance, Web Services Compression and Reliability, and Reliable Web Services). Two of those are MTOM and XOP. Now a customer wanted to know if WebSphere supports these.
I've also talked about the WebSphere Software Early Programs, one of which is (or at least was) the WebSphere Application Server Feature Pack for Web Services (which now has support). This feature pack is no longer in beta, it's GA (generally available); so it may no longer be considered an early program, but it is now supported for production use.
The Web Services feature pack adds support for MTOM and XOP (as explained in the info center). The package is WS-I compliant. It implements the WS-I Basic Profile 1.1. However, BP 1.1 is older than MTOM/XOP and so doesn't include them. WS-I BP 1.2 does include XOP 1.0 and SOAP 1.1 Binding for MTOM 1.0, but it's not final yet. The MTOM/XOP support in the WAS feature pack is compliant with latest draft of WS-I BP 1.2 (March 2007), which is about as close to standard as we have right now.
There was also a question about interoperability with Microsoft products. I can't speak for Microsoft (or IBM for that matter!), but Microsoft generally claims that their products are WS-I compliant. If so, then their products should eventually support WS-I BP 1.2 and therefore support MTOM and XOP. WS-I compliance also means that products from different vendors (such as those from IBM and Microsoft) are supposed to be interoperable. (See Interoperability vs. Integration and More on Interoperability vs. Integration.)
So: Yes, WebSphere now supports MTOM and XOP. To get it, install the WAS 6.1 feature pack for Web Services.
Update (Aug. 15): Note the comment from IBM's Billy Lo: He gave a presentation at Impact 2007 that demonstrated MTOM interoperability between WebSphere and Microsoft products.