If you are running a ShoreTel System (at least in Germany or Switzerland) and you have some people forwarding calls to external phones like mobile phones and/or land lines. They may not see the incomming caller ID on their external device. They will only see your system default PRI caller ID. This is very bad if these guys miss the call, they cannot call back.
This behavior can be changed since 11.x with a registry hack and since 11.2 it has been integrated much better into the system, but it does not exists by default and leaves you in the rain; if you are not aware of this feature. Until today these settings are not documented in the public.
UPDATE 01/20/2012: We rolled back all below settings, after we have been migrated from Nokia to Siemens EWSD and are now using a Custom Trunk Group Dialing Rule with a value of ;3E only.
In previous 11.x builds this was done by appending a registry hack flip_rnie 0: