Instead of having an individual extension receive the call, you can setup a group of extensions that will ring when someone calls in. Anyone in this group can then answer the call.
True, but it's not really what the topic poster is looking for.
In some situations (like this case) the director will have their own phone number, and they will answer almost all of the calls that call in on that number.. but very occasionally his assistant might need to take one of his calls, even though the assistant's extension doesn't ring for calls on that line (due to the volume of calls and the fact that the assistant answers only very occasionally). So this is where a feature to pick-up calls that are ringing on one extension from another non-ringing extension is useful.
This feature is common to most other PBX systems including Asterisk, and is supported by many IP phones (e.g. the entire Linksys/Cisco range). Unfortunately Axon doesn't support it as of now, and the only way of answering a call from another extension is to also have that extension on the same ring group.
What you can do is set a delay on the assistant's ring, so if the director is not in his office, the assistant's phone will start ringing after a predetermined amount of time (e.g. 15 sec), thus minimizing the disturbance to the assistant during normal day-to-day phone calls that the director answers.