FreePBX upper limit: 10,000 extensions
There was apparently a FreePBX AMA (sort of) back on May 1st that I was oblivious of.
Was just skimming the thread and found this gem.
That's a pretty decently high limit. I wonder how many FreePBX users are in the several thousand range. I think when you are getting that big the interface starts to be a hindrance rather than a benefit. I've never tried FreePBX in that range, but I would guess that working from text files and command line would get to be preferable.