asterisk users - Mar 2004 - ChanCAPI and withheld / unavailable callerid indication

My ISDN phone is able to display "No. Suppressed" and "No.
Unavailable",
depending on whether a caller wittheld their identity or is simply out
of area. I'd like to be able to make the same distinction with asterisk,
ideally within extensions.conf. I've had a look at the chan_capi source
code, but am none the wiser - I don't really know enough about ISDN
signalling, so I don't know if this feature is already available,
missing or if it's not possible to do it for some other reason. Any
thoughts?

Patrick