What is call appearance and line appearance in IP phones?

[Detlef Lechner]

Christopher Chan wrote:
> Detlef Lechner wrote:
>   
>> Hello,
>>
>> Synaptic: "Twinkle is a voice over Internet Protocol (VoIP) SIP Phone: A 
>> softphone for making telephone calls using SIP over an IP network. 
>> Twinkle supports direct IP phone to IP phone communication or a network 
>> using a SIP proxy to route your calls. Twinkle provides making basic 
>> voice calls, and in addition the following features (regardless of the 
>> services that your VoIP service provider might offer): two call 
>> appearances (lines), ..."
>> What is a »call appearance«?  I have found a description but I still 
>> don't understand what a call appearance is: 
>>     
>
>
> Two call appearances just means that you can handle two internal phone 
> lines in the phone system. One of them can be tied to a direct number 
> from an outside line and the other will be your internal extension. Or 
> however the phone system is setup. One could be your extension and the 
> other tied to your voicemail.
>   
Thank you for commenting. But I would like to know more exactly, what a 
call appearance _is_, not only what it _means_.

Detlef