Outgrown Dial Plan

[DAVID BURKHART]

Our organization has recently outgrown the dial plan I implemented in 2000 (yes, Y2K!). I knew it was coming, but I thought I had more time. Now it's here. I've been using four-digit dialing internally, and assigning voicemail-only (no physical phone) extensions in the 6000s and 7000s. 2000s thru 5000s are used for DNs/physical phones, 8 for outside line (used to be 9, but too many 911 calls when people were dialing long distance). 9 is not currently used for anything, but I'm reluctant to use it. Consequently, it seems I need to move to five-digit dialing - at least for these voicemail-only "phones." 

My thought is to prepend a 6 to all the existing 6000 thru 7000 extensions, then start assigning new voicemail extensions at 60000 and increment upward. It has been literally more than two decades since I have had to configure this side of CUCM, and several years since I setup CUC. 

• Does the rationale and resulting decision seem sound, or am I missing something that would be much easier than this conversion?
• If I indeed do need to move to five digits, does transition idea plan seem sound reasonable? All my DID (2000s thru 4000s) would remain four digits. 
• What are the high-level steps or processes that I need to change? For example, I know I'll need to update the voicemail profile; transfer directly to voicemail (*XXXX; create new *6XXXX); use BAT to create new extensions then manually remove old extensions in CUCM and CUC. What am I missing? 

I hope I won't need to read a full Administration Guide to get this done, but I'll do what I need to do. Any suggestions or ideas that may cut down the time to accomplish all this would be greatly appreciated. 

[Roger Kallberg]

It’s not really recommended to create a variable length dial plan as it by what you wrote sounds like you’re planning on doing. This will cause undesirable delays in calling. 

[DAVID BURKHART]

I could move all the extensions to 5 digits and prepend the phone extensions with 7. Other than that, what are my alternatives?

[Roger Kallberg]

The harsh and straight answer is none. You’ll have to bite the sour grape and just dig in.

[Elliot Dierksen · Accepted solution]

You didn't mention 1XXX series. That should be available as you describe your current dial plan. @Roger Kallberg is correct about variable length dial plans, so don't go there. The only possible except to that could be (example only) 1XXX-6XXX are 4 digit and 7XXXX are 5 digit. Then you don't have the variable length dial plan nightmare that roger was talking about. If you have to renumber, you are probably better off just doing it. You definitely need to make a really careful plan and do some testing. If you can, build an offline copy of your cluster (CUCM and Unity) with phones and test the impact before you try and do it live.

[DAVID BURKHART]

I apologize for not marking this as the solution previously. I ended up starting at x1990 and working downward. This enables me to plan for five-digit dialing rather than having an ill-prepared plan rushed into production. Thank you, @Elliot Dierksen!