ANSWER:

Step #1
Server to server communication is NOT enabled when using the default ejabberd 2.0.1 configuration.
You need to turn it on to be able to have Google Talk to connect to your server.

The following config parameter should be set to appropriate value:

 s2s_use_starttls, true.
 s2s_certfile, "/ejabberd-2.0.1/conf/server.pem".
 s2s_default_policy, allow.

In that case, any server will be able to talk to your server. Read guide for other configuration parameters to limit access to your server.

Step #2 (if behind a firewall)
If your server is behind a firewall, then make sure that the s2s ejabberd port is open (5269 is default port).
You may have to open other ports if you are not using ejabberd default port numbers.

Hope this helps

Hilary

hob from http://stackoverflow.com/questions/16633231