Did you program the Caller ID for the sets?
Do they get the CLID before answering the calls?

You do not program Target lines to Appear Only as it is useless to do so. What you call the Prime Line is rather/probably the "main number for the business". Prime Line is actually what a phone will grab when the handset is picked up or when handsfree is pressed.
That Target line should be programmed to A&P only on sets that will handle calls (answering them). Then you select how many Appearances it should have depending on call volume.
or Make the Target Ring Only and assign as many Intercom key as needed again depending on call volume.

6.0 is flaky and should have never been installed with a PRI.

Suggets an immediate upgrade them to 7.1 and make sure the NVRAM is Rls 2.

As for Park yes it can be programmed to a key like any other feature.



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