You must have at least one customer on the Thousands-Block to submit a Part 4 to acknowledge that the resource is in service.  “In service” is defined in the ATIS-0300119, Thousands-Block (NPA-NXX-X) & Central Office Code (NPA-NXX) Administration Guidelines (TBCOCAG) as “A Central Office (CO) Code (NPA-NXX) or Thousands-Block (NPA-NXX-X) for which local routing information appears in the LERG™ Routing Guide, and one or more Telephone Numbers (TN) within the CO Code or Thousands-Block has been Assigned to an end user (FCC 00-104, ¶240).  Numbers that are categorized as Administrative, Aging, Intermediate, Reserved, or Available cannot also be Assigned and do not satisfy the In Service requirement.”