[Asterisk-Users] How to differentiate a *busy* call from not available?

[Jean-Yves Avenard]

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Hello

I'm trying to find a way to differentiate wether a SIP extension is 
currently busy (e.g. on the phone) or not registered.

So i do something like:
exten => 100,1,Dial(SIP/foo,20,tr)
exten => 100,2,VoiceMail,u100
exten => 100,102,VoiceMail,b100

If the phone doesn't answer I get the message: User is not available
if the phone is currently in used i get the message: User is on the 
phone

But if the phone is unplugged, I also get the message: User is on the 
phone!

Any ideas?
Thank you
Jean-Yves
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