No extensions?

I am looking at Asterisk to setup a small PBX for a client (50 users).
Each user currently has their own line (via a very old Audix PBX).
so each user has a line that looks like:

(123) 456 7890 John Doe
(123) 456 7891 Jane Doe

If I understand correctly, Asterisk assigns “extensions” like

(123) 456 7000 ext 111 John Doe
(123) 456 7000 ext 112 Jane Doe

Is it possible to setup Asterisk in such a way, that each user can keep their “line” and number in the manner it is now? If so, can someone direct me to the documents of a “how to”?