Hi Iņaki,
 
  yep I have ;)  Sorry my config is actually with start=yes, but Id gotten so frustrated I even tried running the mediaproxy
portion on a seperate server with only the dispatcher on the OpenSER system (this made no difference to my problem).
In my syslog I see both the dispatcher and the mediaproxy running, and the socket files are created. Sessions are even
started per call as you'd expect but at the end of the call the mediaproxy summary (in syslog) states that it has forwarded
0 bytes/packets of data :((.
So it seems the OpenSER mediaproxy module is correctly making the request to the dispatcher for a proxy session, but
something is not updating the SIP IP and PORT to redirect the RTP via the proxy.... 
 
Any ideas? There seems so little you can configure regarding this in the route that I feel at a dead end...
 
>Have you really read the doc? ;)
>
>; start         Boolean value that specifies if to start the RTP proxy server.
>;               Default value: Yes


>Also, after setting tha parameter to "yes" do a "tail -f /var/log/syslog" to 
>see mediaproxy and proxydispatcher messages.