Hi
Please upgrade the PBX to version 7 if you are still on version 6. In version 6 there was a bug related to this where with certain phones under specific situations call pickup might not work.
The dial codes remained the same - but they are 100% configurable from the interface - (In V7 the dial codes page is located under Settings\Advanced\Dial codes tab
Note: The PBX must be licensed for Dial codes to be enabled