Setting CallerID on outgoing ISDN calls?

Question

Does anybody have any experience of settings the CallerID on outgoing ISDN calls? We are trying to set the caller id to one of the available DDI's on our circuit but without success.

They worked on the previous phone system (NEC) so the feature is definitely turned on by BT.

We are using an OpenVOX card and DAHDI.

We have tried passing the CALLERID(num)= but this just sets the originating CallerID on the trunk to the ISDN channel, and not the actual ISDN CallerID itself.

We have also tried variants of CALLERID(all) and CALLERID(number) without success.

We have also tried the application_dial options of f() and s(), also, without success.

I'm thinking maybe we need to change something in the chan_dahdi.conf or something?