Normally, one should check out three steps for buying EPABX or PBX for their office as follows :

1. Requirement Analysis
2. Benefits of PBX System
3. Choice of PBX Company

1. Requirement Analysis
a. Find out how many people should be speaking within the office premises at any point of time as well as how many people need a dedicated telephone connection.
b. If you make lot of outgoing calls then, most probably, you need LCR ( Least Cost Routing) to minimise recurring telephone bill.
c. Depending on power supply condition in your office area, decide on suitable battery backup.
d. Do you need IVR or CTI applications using which you may be able to automate office calls.

2. Benefits of PBX System
a. Decide how incoming calls would be attended by office staff.
b. How many long distance calls are being made or are there any misuse of this. EPABX is capable of restricting long distance calls depending of seniority of staff.
c. How to integrate CTI with your CRM software if you have any.

3. Choice of PBX Company

a. Buy PBX only from authorised distributor or dealer of PBX manufacturer. This will ensure support and service as well as new PBX equipment with proper warranty.
b. Ask for reference and any benchmarking of working of the PBX model you decide upon.