[asterisk-users] Youmail RDNIS

[Karl Fife]

Does anyone know the mechanism by which companies like YouMail (and MNO's 
using their own voicemail system) are able to redirect ALL calls from a ALL 
subscribers to *just one* voicemail DID, yet determine WHICH subscriber did 
the redirection?

I had always assumed this was simply done using RDNIS.  In other words, the 
original calling party's CallerID is passed with the redirected call, (and I 
assumed) the redirecting subscriber's number was passed via RDNIS--thusly 
the voicemail system knows to place the call into the voicemail account 
belonging to the RDNIS value.

In practice I find that YouMail, when presented with a redirected call as 
described above ignores the RDNIS value and prompts me for an subscriber 
account number.  By contrast, when various MNO's do the redirection, YouMail 
is able to determine the redirecting subscriber account number--presumably 
some other way.

Does anyone know the mechanism(s) by which this is normally done?  Is there 
even a 'normal' way to do this (such as a QSIG call transfer message), or is 
truly home-spun and carrier-specific, such as a Q.931 facility message.  Any 
advice on the subject would be much appreciated!

Thanks!
-Karl