Sizbut.
I'm sorry, was a bit short.
It's a virtual IP Office release 11.1 sp1. J169 phones.
But, I already found the issue.
It seems that from R11.x you need to enable the users in the call pickup group.
Then, when you program a 'pickup member' button for that group. The button even flashes during a call to another member, indicating a call is present at another extension. (finally Avaya added this feature)...