In the olden days, because we bought up a lot of small sites and merged them all together, my dial plan was all over the place. In 920 area code we had 682, 683, 684, 686 and 652 numbers - the last 4 digits were what was being sent by the phone company and that's what matched our extensions.
In this scenario, say someone paged you to extension 4456. You needed to carry around a cheat card to tell you which one of the 5 NXX prefixes you had to dial to get that extension - it was a confusing mess.
In 2005 I petitioned AT&T to sell me a "K-block" of numbers. That means they would request a whole new block of 10,000 numbers from the national licensing organization (NeuStar). The end result would be that any extension in my organization (in this city) would start with an NXX of 320. In general numbers are considered a priceless commodity and are very stingily guarded.
NeuStar denied AT&T's request to obtain the numbers for me. I then had to petition the Public Service Commission of Wisconsin and appeal the ruling, stating my valid business reasons for needing the numbers. I explained that my plan would be to overlay the 320 numbers over my existing dial plan for 6 months (to give us time to educate the public and revise our printed materials) and then I would release all of the original numbers back into the number pool for future re-use. This would work because the phone company was only sending me the last 4 digits (I have 4-digit extensions) so the switch could care less if the NXX was 682, 683,... or 320. As part of my negotionation I agreed I did not need any of the 9000 numbers (because dialing 9 is reserved), 1000 numbers or 7000 numbers (because I had no extensions in these blocks) and 8000-8399 (because 80, 81, 82 and 83 are used for paging, etc applications).
The end result was the PSC overruled NeuStar's decision and granted me the 5500 numbers I asked for because I had a valid business reason for it. I got a nice raise and consider it one of the crowning achievements of my career so far.
It doesn't matter what equipment you have as long as you're using 4-digit extensions. Now things get stickier if you are only doing 3-digit extensions and you're trying to find a continuous block of 1000 numbers (say 5000 - 5999) so you can match up all your extensions. Phone companies are either really random with how they give out their numbers or they will absolutely refuse to open up a new block of 1000 numbers until the others are used up - they only get so many and they try to save the bigger blocks in case a larger customer needs a number pool, or for other special purposes - it can be hard to find 100 contiguous numbers in some cities, much less a really big block.
Keep in mind I still had to pay installation charges for each block of 20 numbers and I still do have to pay the monthly charges for them, so this was not without cost, but the long-term benefits of having a unified dial plan was really a no-brainer as far as payback is concerned.
Good luck. The place to start is your phone compnay and try to get them to go to bat for you. Try to have a well outlined list of points to justify your need for them and how your business growth would be affected, etc... If they don't want to cooperate go over their heads to the PSC and explain your need to them and that your phone company refuses to work with you - maybe they will help.
If you don't have a concrete, valid business reason that can be clearly shown for why you want a big block of numbers, don't waste your time.
Good Luck