Inexpensive PBX?

Question

ATS

There is a small office.
Two phone lines, four office phones.
I want an easy way to use both lines from every phone in the office. Those. when one line is busy, outgoing on the second line.
There will only be two lines.
What are inexpensive pieces of iron to solve the issue?
Ideally, the ability to receive statistics on incoming / outgoing calls for a period.

Answer 1

how many internal subscribers? because this is also very important.

Answer 2

Panasonic KX-TEB308 I think you should be satisfied.
Simple, reliable, easy to set up and administer. The basic model (without DISA [automatic attendant] and CallerID [AON]) costs less than 10,000 rubles.

Answer 3

But didn't you look at it? habrahabr.ru/blogs/telephony/109836/

Answer 4

Panasonic, above called. If 300 bucks is expensive, there are maxicoms. Oak, but they work.