Thank you for using the ADTRAN Support Forums.
Actually, under the ATLAS Dial Plan, every entry is independent, and ATLAS acts as a switchboard to route calls through from one interface to another. In the DIAL PLAN, the interfaces are configured based on what they are connecting to. So NETWORK TERM connects to the PSTN Network, and USER TERM connets to your user equipment.
By configuring the NETWORK TERM as a "National ISDN" switch type (in the ATLAS this is NI-2), and the USER TERM for Lucent 5E, and the ATLAS will "translate" between them when processing calls through.
(This is done quite a bit in Canada to convert DMS-100 to NI-2.)
Hope this helps,