Two clients I worked with insisted me to deal with their PBX system.
The first one was the Merlin Avaya system. Took a while to reach success. The second one has Nortel BCM50. That's a pain since Nortel is so paranoid they make these require a license called "Keycode" for different situations, companies, etc.
Thus I was being "motivated" to research more about the PBX phone systems. Learned a few interesting things. I'm surprised however, that with all the networking technology today, these PBX systems or the systems for phone networking could cost so much as thousands of dollars in equipments as well as licenses (for some, like Nortel).
Then There's the open source Asterisk. Which is a PC server PBX based mainly on Linux (or Mac, maybe Windows). However, I still find it a bit too much.
Since I am dealing with the requirement of more than 1 pots/FXO/Analog lines, I am more obliged to look into SOHO's PBX systems, which cost as little as $250-$300 on Ebay, supporting 4-8 analog lines, 16-32 extensions, on just one box.
Of course, there are the cheaper 2 POTS to 8 extensions (also by SOHO) for $70.
Well, since the last client, under my urge, has decided to go with a professional tech on this issue (instead of...me), I will just keep this information for my own future reference.
Now it is a hard thing for me to just waive all the time I've spent hoping to somehow get it done on my own. I was worried, since the first time was too time consuming. Perhaps both I and the client thought I could make it work again. I underestimated Nortel.
Youtube and Ebay are good sources of help.