It seems that Jitsi's presence status (global and per-protocol provider Online, Offline, Do Not Disturb, etc.) is only used to "publish presence" but not to actively reject a call on client side. For instance, if the user sets global status to "Do Not Disturb" (hence DND status is set for each protocol provider) then CallManager -> GuiCallListener -> incomingCallReceived should check the "global presence status" (although it doesn't seem to be implemented so maybe loop through each provider, check each status and for each one send a "BUSY HERE" or "CONGESTED" or "UNAVAILABLE" message back via the protocol provider implementation). So, if I set "DND" in my SIP account and "Online" in my Jabber account then an incoming XMPP call should connect but an incoming SIP shouldn't (and an appropriate SIP reply should be sent to the caller).
Anyone considering this as useful?
If so, can I post a feature request on JIRA?