What is the best way to organize internal phone numbering in a small chain of stores?

Question

Telephony

Good afternoon,
We have Asterisk and there were five stores, internal numbers started with 100, 200, 300, etc., and in general everything was fine. But now we are starting to open new stores and there are more people, and we decided to redo the numbering plan, but the question is how best to do it ... According to the store plan, there are more than 10 stores, and departments have been formed, such as "Store Managers", "Accounting", "Purchasing Department ", "Protection", "Production", etc. And now we are thinking about how best to organize the numbering, maybe someone has already stepped on this rake?

Answer 1

100.. Administration (general) 110.. Administration (managers) 120.. Administration (accounting), etc.
200-209 Hoof Horn Shop 210-219 Hoof Horn Shop and so on. You can give fewer numbers to the store. For example 200-250 for shops. 251-300 Purchasing department. 301-350 Manufacturing.
Look at the number of rooms you need with a small margin.

Answer 2

We just had a problem that the departments began to "smear" around the stores, before they were in the same office, now Purchase, Production are in every store ...

Answer 3

Allocate 50 numbers per store, not 100. Business.
Ignore departments.