Need a telephone connection between four employees, what to put?

Question

Telephony

Dear forum users!
Please tell me how to solve the problem correctly and not expensively:
A small office, you need a telephone connection between only four employees,
you don’t need an exit at all (yes, don’t be surprised) :)
I have no practice in the field of telephony, but I have an idea, because I work in the field of network administration.
Need some advice on what to buy?
The wireless option is no longer available. the location of offices on three floors is not good.

Answer 1

Asterisk (as an option, with a body kit in the form of FreePBX) and softphones for employees. UPD: if IP telephony is not suitable, a DECT base and four handsets with intercom function.

Answer 2

You can use a regular 4 port FXS gateway. Set up short numbers (101,102,103,104) and enable the use of the local phone book (routing). TA can be used ordinary copper.

Answer 3

some phone models allow you to work without a PBX and connect to each other using IP addresses. maybe it will be easier for you at first.

Answer 4

Who buys telephony equipment on what site?
You can share good, proven sites.
Soon we will have to choose another 40 IP phones and PBXs for another task.