I just had this come up with a customer. While this is not clear via the documentation, it is intended behavior. Listening to a call means you have to be in a status that can receive a call. That means you must be available or away (set manually, not from idle, screen saver, or lock screen). All other statuses will go to Voicemail and fail.
As an additional note, while I don't know of a way to prevent direct DID or extension calls, you can prevent group calls from interrupting your users who are listening by using the forward feature. Instead of putting in a remote number, make the first forward box your desk, web, or whatever use normally use. This will still allow you to listen (as long as your status is available or away) but you will not get group ring calls.
Thanks,
Daniel McLeod
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Daniel McLeod
Qsect LLC
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