Funny you should ask.

http://xmlrpcflash.mattism.com/ is for AS 2. I converted it to AS3,
fixed some bugs (maybe introduced new ones :), and it seems to work
for me. I was going to seriously clean it up before annoucning,
but since you ask, here:

http://www.hrum.org/people/debedb/pro/blog/2006/12/xmlrpc_in_flex_2actionscript_\
3.html