Good evening.
I have succesfully configured mod_callcenter (queue, agent and tiers) in my freeswtich with agent behing a trunk sip (all the extension are reachable from FS but are not registered in it), all work as intended.
So the simple configuration of the agent is:
    <agent name="agent999" type="callback" contact="[call_timeout=10]sofia/gateway/gatewayName/999" status="Logged Out" max-no-answer="3" wrap-up-time="10" reject-delay-time="30" busy-delay-time="60" no-answer-delay-time="10" />
All work well and i get the right agent status and agent state.

But this work only for the inbound call routed to freeswitch, i haven't any information abount agent independent presence (For Example: if the agent dial and is in call with another agent) .
So the internal database "think" that the agent is available and ready even if is in call and busy so the mod try to invite him obviously whitout success.

I  try in the gateway to subscribe whit the presence of remote agent, and in some way update internal database with script lua or event_socket
<include>
  <gateway name="server_gw">
    <param value="no-reg" name="username"/>
    <param value="server.org" name="realm"/>
    <param value="no-reg" name="password"/>
    <param value="10.0.80.10:5060" name="proxy"/>
    <subscriptions>
        <subscription event="presence">
            <param name="content-type" value="application/pidf+xml"/>
            <param name="expire-seconds" value="60"/>
            <param name="retry-seconds" value="30"/>
            <param name="username-in-request" value="true"/>
        </subscription>
    </subscriptions>
      ...
I haven't found a way to subiscribe and receive the notifiy and publish event of prencence in the gateway (trunk sip) for a specific group of agent, in my example the extension 999 behind the trunk (but ideally all my call center agent), the subscribe is from and to "no-reg" for a contact gw+server_gw, i need to subscribe to someting like 999@server.org

  SUBSCRIBE sip:sa@server.org:5060 SIP/2.0
   Via: SIP/2.0/UDP 10.1.10.82:5080;rport;branch=z9hG4bKU3DyKZaHrg24p
   Max-Forwards: 70
   From: <sip:no-reg@10.0.80.10:5060>;tag=K3N8p1cKmS1vm
   To: <sip:no-reg@10.0.80.10:5060>;tag=e340d29f4e69500c4c17ab56fb041ae6-7cd3
   Call-ID: 1db94e51-298b-1234-1493-005056963714
   CSeq: 85401361 SUBSCRIBE
   Contact: <sip:gw+server_gw@10.1.10.82:5080;transport=udp;gw=server_gw>
   Expires: 60
   User-Agent: FreeSWITCH-mod_sofia/1.7.0+git~20151210T010223Z~85f8bca628~64bit
   Accept: application/pidf+xml
   Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY
   Supported: timer, path, replaces
   Event: presence
   Content-Length: 0


There is way to subscribe through a trunk for presence or generate it via mod_event_socket ( i found only the NOTIFY event and not for SUBSCRIBE https://freeswitch.org/confluence/display/FREESWITCH/mod_event_socket#sendevent), or there are any other tools to probe the presence and don't do a "polling of busy call" for a call center application?
thank you for all, and thanks indeed for the help receveived in the past month.
Emiliano Olivier