Showing results for 
Search instead for 
Did you mean: 

4 digit dial plan - extensions starting with zero '0'

I have a client using CUCM 7.x that wants to use a 4 digit dial plan as follows:

  • basement:  0000-0999
  • 1st floor: 1000-1999
  • 2nd floor: 2000-2999
  • 3rd floor: 3000-3999
  • 4th floor: 4000-4999

You get the idea.  They have a total of 7 floors.

While technically this can be done and would work I need reasons why this should or should NOT be done.

Any thoughts?  Moving to a 5 or 6 digit dial plan is not an option.  Don't worry about DIDs - that already own the entire exchange (0000-9999).


Hall of Fame Community Legend

Hi Andy,

The are no inherent issues with using "0" for extensions. The main

things to consider are the inability to use "0" for your Operator

and for people who mis-dial any Off-net access codes that begin

with zero. Other than that you should be fine here. We used extensions

that begin with "0" in our Campus residences without any problems




Like Rob said, you can do will work.  Often times companies will reserve "vanity" numbers for future use and delegate other things out.  One thing to consider though is scalability and overlap.  Let's say that this works great now but in a year or two (take your pick), Company XYZ grows and picks up another office location down the street and want to centralize on the existing cluster.  Let's say they also "insist" on 4-digit dialing at the new site or between offices and all or even part of the DID range purchased for the new location overlaps with the existing dial plan.  Granted, this may never happen but I point it out because I've seen it before and, in fact, my company is often called upon to clean up dial plans that have issues or just don't scale.  So, you could consider a multi-tenant design and base the root of the system configurations on a full 10-digit dial plan.  What does this do for you?  Well, if done right - you can offer the best of both worlds now and simplify things in the future.  With a single translation pattern, all users could dial 4 digits now while the system handles the full NANP number in the background.  When Company XYZ expands, the new office users can dial 4-digit as "insisted" within their buidling as well.  For inter-tenant calling, you could use a site code (or digit) + 4-digits or just treat calls as 7-digit or 10-digit local (based on local dialing plan) but with calls traversing the WAN/MAN as opposed to the PSTN (which could be used as a backup).

Just some thoughts...


Please rate helpful posts!


Initially  first install all good then you start to move users around different floors and the whole prefix per floor disappears- yes the IT person will say now the number stays at the desk but Mr Big states that everyone has their number so it must stay with me !!!!!. What happen if whole teams move? I would not worry about the Prefix per floor. I would look to towards the future as others have mentioned and look to make use of Site codes but mask out the Site code when dialing within the same building/ location  so users do not need to worry about it but the important thing is you have already configured it. If you go down the route of Site codes then you need to think of the access code. Either use a prefix no-one currently uses or maybe * or # prefix as the access code so you can still use all the 0- 9xxx range. if you use * or # be aware of analogue feature codes and who uses the analogue DN. If they are for faxes then not a problem, for simple phones then again maybe not a problem - how many people will know the feature code of transfer and to be honest who will use it. Most analogue devices if they are used, are  for door entry, comms rooms etc are just there to be able to make and answer calls so potentially no big deal