dagwoodsystems

You're thinking of a feature called "Group Ring", which was not available until Release 3. To make it work, select Group Ring as the Calling Group's hunt type, then add up to 20 extensions as member of that Calling Group. Dialing the group's number causes every phone in that group to ring simultaneously.

To make this work with a PRI, one of two things could be done. First, you could simply renumber the Calling Group to match the digits sent with the associated DID number. Alternatively, use the Inbound Routing table to manipulate the digits sent by the telco (used when these digits don't match anything in your dialplan).