asterisk users - Oct 2007 - DUNDi, regcontext, softphones.. fail. :(

All,

I'm having an issue deploying softphones into my DUNDi/regcontext
setup.  My current design is that all SIP users get registered into a
sipregistration context in the sip.conf.  I then have a dialplan
function that includes that and does the dial:

include => sipregistration
exten => _XXXX,2,Answer()
exten => _XXXX,3,Wait(1)
exten => _XXXX,4,NoOp(sipregistration call - Name: ${CALLERID(name)}  Num:
${CALLERID(num)})
exten => _XXXX,5,Macro(stdexten,${EXTEN},SIP/${EXTEN})  ; 913-563-77XX

This works really well for hard phones.  They register, exist in the
sipregistration context and are dialed on whichever server they register 
by DUNDi.  I only started to run into problems when I had to deploy softphones.

The softphones register when they are up and running, and the system 
works as designed.  But when they close their softphone, there's no way 
for the system to know where the extension is, so the call dies.  It 
doesn't go to voicemail like I would like it to because that extension 
never proceeds through my dialplan.

Looking for suggestions on getting around this so I can keep deploying
soft phones to agents in the field.

Thanks in advance!

-- 
Kyle Sexton