If calls to destinations outside the IP network are failing, it may be because the calls must be routed through non-Cisco PBX switches that are connected to the PSTN. In order for the Cisco Unified Communications Manager to properly direct calls out trunks on the PBX, proper interoperability configuration is required. Information on configuring PBXs to interoperate with Cisco devices is available on an Interoperability Portal 
site. This site has information on third-party PBX interoperability with the following Cisco Unified Communications products:
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Cisco Unified Communications Manager
•Cisco Unity
•Cisco Unified Contact Center Enterprise
•Cisco Unified MeetingPlace
The information is provided in a series of application notes. If you cannot find your exact configuration in the list of available application notes, you may be able to use other application notes to meet your needs. Here are some suggestions:
•PBX product families should have similar results. For example:
–PBXs in the Nortel Meridian 1 family should have similar results. The Nortel Meridian 1 Option 11C will have similar configurations as the Nortel Meridian 1 Option 61C and the Nortel Meridian 1 Option 81C.
–PBXs in the Avaya Definity G3 family should be similar. The versions VSI, R, CSI, and SI should have similar configurations.
–PBXs in the Siemens 300 family also should have similar configuration results. This family includes the 330, 340, and 370.
•Gateways configurations should be similar if the gateways are Cisco IOS based and have the same protocol (for example, MGCP, H.323, or SIP). For example, a Cisco 2801 gateway should have similar configurations to the 3845 when used with the Cisco Unified Communications Manager.