AT&T Clec Online

Handbook for Arkansas, Kansas, Missouri, Oklahoma, Texas

Direct Inward Dialing

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Product Description 

Direct Inward Dialing (DID) is a feature of some Private Branch Exchange (PBX) systems. This feature allows incoming calls to be dialed directly to PBX stations, bypassing the PBX attendant.   

DID trunks are always one-way trunks (incoming calls only); never Touch-tone.   


DID service is available in most Electronic Switching System (ESS) and Digital Central Offices (COs). Two items must be in the CO to provide DID service:   

  • Network facilities (trunks)     
  • Telephone numbers

Contact the Local Service Carrier (LCS) to determine if trunk facilities and requested quantity of DID numbers are available in the CO.    

  • DID numbers are available in blocks of 10 or 100 to be single number      
  • The End User (EU) needs to provide signaling, pulsing, start dial, and the number of digits to be dialed for DID's

Two new service options have been added.  These options are effective: 

  • June 1, 2002 in Missouri and Texas
  • June 6, 2002 in Kansas
  • July 1, 2002 in Arkansas and Oklahoma

Reinstate DID numbers into a DID Block 

  • Provides the ability to add back individual DID numbers to the original number block.  The reinstatement of DID numbers, for use by the same end user, is offered subject to the availability of facilities.

Pointing a Business Access Line to a Digital Trunk 

  • Provides the ability to point an Access Line number, via a route index, to a digital trunk (eg SuperTrunk). 

Temporary Removal of Numbers for DID Block

  • This additional option is available in Texas.
  • Provides the ability to temporarily remove numbers from a DID block. 
  • The temporary removal of a number(s) from a DID number block, for use by the same end user, is offered subject to the availability of facilities.
    • In such cases, the end user shall continue to pay the appropriate rate from the original number block of DID numbers.
  • When a block of DID numbers or when the temporarily removed number is disconnected, all numbers which were temporarily removed must be returned to the original block of DID numbers.


DID trunks have the following limitations:   

  • Custom Calling Service (CCS) - Simultaneous Call Forwarding is not available       
  • The Power Failure feature on PBX systems will not work with DID trunks

    Note: If a power failure occurs in the CO and the end user has only DID trunks to handle incoming calls, no incoming calls can be completed.


DID orders are placed on LSR REQTYP T. 


Refer to the USOC Search Tool for additional information on USOCs.

DID Reinstate

First and Additional Numbers


Point Access Line to Trunk

Service Establishment


Per DID Number


PRI ISDN Number Blocks

10 Number 1st



10 Number Additional



100 Number 1st



100 Number Additional



LSR Examples for this product may be found in:

DID/PBX Resale