By default, systems with a U-Law System SD card default to using a 9 prefix for external calls. Systems started with an A-Law System SD card default to no prefix (any dialing that doesn't match an internal number is assumed to be an external number).
Where a prefix is used for outgoing calls, that same prefix needs to be added to trunk settings. That trunk prefix is then used as follows:
•Incoming Calls
On incoming calls, the trunk's set prefix is added to any incoming caller ID received with the call and stored in the call log on phones, etc. The prefix should be such that the resulting caller UD can be used by the systems phones and applications to make return calls. For example, if the system is configured to require a 9 to indicate an outgoing call, the trunk needs to add a 9 to the incoming caller ID so that that ID can be used for return calls.
•Outgoing Calls
On outgoing calls, the short codes used to route the call to a trunk must remove any external dialing prefix (for example 9) so that the number dialed from the system to the trunk is suitable for routing by the trunk provider.
To set trunk prefixes using IP Office Manager:
1.Within the IP Office configuration, select 
Line.
2.For each line enter the prefix. The location of the prefix settings varies for each trunk type. Some trunk types have a single prefix field. Other trunk types may have separate prefix fields for national, international and other calls.
3.Then either:
•Continue the basic configuration using the following sections of this chapter and then save the configuration when finished.
•Save the configuration as it currently is. This may cause the system to reboot, the save menu will indicate if that is required. After saving the configuration, reload the configuration and continue with configuration.