Nortel Meridian Meridian 1 Feature Description And Administration page 1559

Multiple callback queues are allowed per trunk group for the Conventional
Main by dialing up to 7 digits (any digits are allowed) based on the
availability of Meridian 1 call registers.
Conventional Mains must not allow RVQCM callback calls to be
modified by call transfer or call forward to an outside line. Call
modifications like this can result in the TIE trunk not being released at
the end of the call.
International ISDN PRI Feature description and administration
Remote Virtual Queuing
CAUTION
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