asterisk users - Jun 2004 - If IAX client is not logged in/registered, Dial plan executes BUSY vs UNAVAILABLE

If I have an IAX client (Firefly softphone in this example), and the client
is not registered at the moment because they are not connected to the
network and someone dial that extension, they get the user's "I'm
on the
phone at the moment" message vs. the "I'm unavailable"
message.  Is this by
design?

Here's the extension in question's dialplan:

;extensions.conf  

exten => 106,1,Dial(IAX2/nikko,20,tT)
exten => 106,2,Voicemail(u105)
exten => 106,3,Hangup
exten => 106,102,Voicemail(b105)
exten => 106,103,Hangup

And here's the CLI debug:


pbxMobile*CLI> 
    -- Executing Dial("SIP/nmartin-aeca",
"IAX2/nikko|20|tT") in new stack

pbxMobile*CLI> 
Jun 14 10:28:26 NOTICE[4997140]: app_dial.c:554 dial_exec: Unable to create
channel of type 'IAX2'

pbxMobile*CLI> 
  == Everyone is busy at this time

pbxMobile*CLI> 
    -- Executing VoiceMail("SIP/nmartin-aeca", "b105") in
new stack

pbxMobile*CLI> 
    -- Playing 'voicemail/default/105/busy' (language 'en')

pbxMobile*CLI> 
    -- Playing 'vm-intro' (language 'en')

pbxMobile*CLI> 
  == Spawn extension (Outgoing, 106, 102) exited non-zero on
'SIP/nmartin-aeca'

pbxMobile*CLI> 
    -- Executing Hangup("SIP/nmartin-aeca", "") in new stack

pbxMobile*CLI> 
  == Spawn extension (Outgoing, h, 1) exited non-zero on
'SIP/nmartin-aeca'

pbxMobile*CLI> exit 
Nik