asterisk users - Dec 2006 - bridging calls on a samsung pbx from asterisk

I have the following configuration:

VoIP Provider <----> Asterisk <----> Samsung PBX <---> PSTN
                          ^
Asterisk has a few VoIP extensions connected, but most of the extensions
are hanging of the Samsung PBX.

Asterisk has 1 NT and 1 TE interface, which are connected to a TE and NT
interface respectively on the Samsung PBX. This allows us to use the
VoIP extensions on Asterisk to make calls to the PSTN, and the Samsung
extensions to make calls via the VoIP provider (dial 0 to get PSTN
dialtone, and 80 to get VoIP 'dialtone').

One feature I'd like to add is to be able to use a workstation (outlook
contacts etc) to start a call between an extension and an outside number
(or another extension?), so that Asterisk would ring your extension, and
when you picked it up it would then dial the outside line and then
connect the channels together.

I believe the above feature is all a solved problem under Asterisk, but
in my case a Samsung extension to PSTN call would tie up 2 ISDN channels
(1 on the NT interface, 1 on the TE interface) for the duration of the
call... is it possible for Asterisk to instruct the PBX to internally
bridge the calls together, and thus get Asterisk out of the call path?
 
I guess it would have to be a function of the ISDN protocol to allow
this sort of thing... I'm pretty sure I read somewhere that you can do
this if they are both on the same ISDN interface but these are on
different interface, and actually different adapters - the NT is a
HFCS-USB and the TE is a NetJet.

Thanks

James