I'm not as sure of the way a 200 works with Auto-Answer enabled.
I suspect it is the same as the 3300 where it would require the Mic to be "Pre-Engaged" to allow 2-way calling.
This is definitely the case when using Directed Paging as the manual state as below.
This feature allows users to respond handsfree to a directed page. In order to respond handsfree, the user must turn on the set’s microphone in advance. Then, if a directed page is broadcast over the user's set, the set microphone is activated allowing the user to speak handsfree to the calling party.
The called party is alerted to the page by a short tone. Also, depending on the set type, the MICROPHONE key LED will flash or the MUTE key LED will flash rapidly.
The Manual is not as clear with respect to the Auto-Answer feature.
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Occam's Razor - All things being equal, the simplest solution is the right one.