The most useful thing I like about SOAP vs REST is the WSDL. It makes my life much easier when creating applications for the iPhone as my classes can be generated for me without me doing much monkey work.
However, I'm trying to find a suitable alternative to ASMX/WCF. I predominantly use a Mac so Java, PHP or Mono solutions are mainly of interest to me.
I understand PHP has a SOAP service offering but it can't automatically generate a WSDL? Are there any tools which can facilitate this?
There are many java based soap stacks. I would look at Apache CXF (http://cxf.apache.org/). See also its WSDL generation at http://cxf.apache.org/docs/soap-12.html.
The latest versions have pretty good support for WSDL.
http://php.net/manual/en/book.soap.php
Here's a quick guide for it:
http://www.phpbuilder.com/columns/adam_delves20060606.php3