Snom 320 - Manual (Page 86)

86 • Settings
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Phone Behavior
Call Completion: Turning this setting to “on” will prompt the user
to activate call completion, if possible, while calling a number (see the CC
soft key). When the called party becomes available again, your phone will
be able to automatically redial the number. CCNR (on not reachable) as
well as CCBS (on busy) is supported.
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