What I mean are those fixed, built-in extensions like: 70 or 88 ? When you install 3CX you get warned that about 30 numbers are being reserved for system extensions so I'd like to know which 30 and if the can be edited. ###edit### Let me add a related question: When installing and selecting i.e. 2 digits for extensions it says usable from 10-99 but that is plain wrong I didn't read that and successfully assigned 00 as my main number for reception then assigned 01-07 to different test users. How come?