Is there "event-based" server side asynchronous web method pattern?

[Morgan Cheng]

Since ASP.NET 2.0, asynchronous web service client can be implemented
with event-based pattern, instead of original BeginXXX/EndXXX pattern.
However, I didn't find any material about event-based server side
asynchronous web service. So, we can only implement asynchronous
webmethod with BeginXXX/EndXXX pattern, right?

The only server side asynchronous web method post is
http://msdn2.microsoft.com/en-us/library/aa480516.aspx.

I don't why ASP.NET 2.0 don't provide event-based server side
pattern.

-Morgan