Trunk SIP with IPOffice IP500

I have an Avaya IP500 R5.0 connected with trunk SIP to Freepbx. In Freepbx I have some SIP phone. This sip phone need use the ISDN trunk in the Avaya IPOffice. If i call an extension Avaya from sip phone in Freepbx the comunication is OK.
Have you an idea?
Sorry for my English…

Create an outbound route which whill send the call to the Avaya SIP trunks. Insert “9” or whatever is needed for the call to get out once it hits the Avaya system.

thanks for your answer.
I have create a short code but is no ok. In IPOFFICE i create an inbound route for call from trunk sip. The destination il . because i need to call the avaya extension. For example, 2XX are SIP phone in freepbx, 7XX are digital statiom in Avaya ipoffice. Digital station need to intert “0” to outbound call. In freepbx, in extension.conf i insert a command for outgoing to sip trunk for every call with first number “0”.