When you set an extention up for DND on busy, it will enable DND while the user is on the set. The second call should still go through to the set, although the set will not ring.
Ensure that the extention has at least 2 intercoms to allow a path for the 2nd call.
When you program the DID to have 2 appearances on the set, you will tell the system whether you want it to "appear & ring", "appear only" or "ring only". This setting will affect both appearances. If the user is on the DID, and someone else calls the same DID, it will produce a busy signal (just like a single dedicated analog line without call waiting).
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