1. At least 1 incoming telephone line
2. At least 1 program-controlled telephone exchange. (At least 2 in and 4 out, or 4 in and 8 out, depending on the number of people in the company )
3. At least 1 telephone. (A device with 2 in and 4 out can answer 4 phones, and so on.)
That’s it, you just established a company 400 to call the repair center. Currently there are 4 phones.