Requesting Advice on Asterisk Project Plan


I am new to asterisk and I want to replace an old AT&T Partner phone system with an asterisk system.

The old system is over 30 years old, and the voicemail crashed a month or so ago. I believe that it’s just a matter of time before other components of the system begin to fail and I want to get a jump start on upgrading the system. I was told about asterisk as a good option, and I have been reading about its features, system requirements, and installation procedures.

I wanted to get some expert advice on the conversion. I think I have a couple options. I could try to replace the whole system from start to finish, or I could begin by replacing just the voicemail portion and then expand to the rest of the system. As a non-expert, I think it is probably better to go all out and replace the whole system rather than trying to integrate different systems together. The effort to get both to play nice together might not be worth it. Please let me know if you agree.

My plan is to obtain a box, based on the system requirements detailed in the documentation, using Ubuntu, download the software, build it, then get the appropriate cards and ip phones to work with the new system. Of course, I would have to replace the old wires with those that are compatible with the system.

So, does my newbie approach sound sensible or should I be viewing this project differently? It would also help if you could advise on the best, inexpensive equipment to support the system.

I basically need a system that would support 3 telephone lines, 13 phones, voicemail, intercom, and conferencing.

I hope that I didn’t sound too ignorant in my comments, and I thank you for whatever information that you can supply.

Depending on what type of interface the voicemail module has to the rest of the phone system, what you’ll need to buy to replace the voicemail system will be the same as what you’ll need to replace the whole system (apart from the phones).

In my experience, it is best to just let people know that “on X date, we will be throwing out the AT&T PBX and replacing it with a new system” and provide them with documentation on how it will all work & be different. Otherwise, you’ll end up with a weird hybrid system that doesn’t work completely like Asterisk or completely like the AT&T system.

For such a small system, you’ll just need a run-of-the-mill PC and some IP phones. Then you’ll need someway to get your phone lines into the system, either through a PCI/PCI-e analogue card or through a SIP gateway system.

Thank you for your response!

Sounds like a plan. Thanks for the advice. But, run of the mill? I thought I would need at least a 3 GHz processor and 3 MB of Ram. That is probably run of the mill these days, but I think I read that I would need at least that for multiple users/calls/extensions, is that true?

With 3 lines and 13 phones, you’d have to go out of your way to find a machine slow enough to not run it. 2Ghz processor, 4GB of RAM, and you’ll be set.

Thanks! If you’re also monitoring the installation and other forums, I’ll be looking out for you. I’ll keep you posted on the progress.


Hi again, quick question. I found a box that has 2 G RAM and a dual core processor but only has 1 PCI slot. For the system describe before, do I need more PCI slots? How many extensions can hold on one PCI card? I need 13 extensions.


Extensions don’t use slots on SIP, they just go through the ethernet port. You’ll be using SIP internally no matter what protocol you’re using to get to the PSTN (the outside world). I would caution you, however, that if you’re using POTS lines, you will need to have an appropriate slot to accommodate the interface card, so figure out what you’re going to do about that before buying a server.

I would also recommend buying a used “real server” rather than a souped up, new desktop machine. Such a small Asterisk installation isn’t going to put too much of a burden on your CPU. The advantage to a real server, even if it is several years old, is that it has lots of redundancy - two power supplies, RAID hard drives, etc. - which will greatly decrease the probability of downtime. Our Asterisk installation is on a system with SCSI RAID, set up so that even if one of the hard drives crashes, the phone system keeps on working.

This might also be a good time to reevaluate your needs in terms of outside lines, DIDs, etc. You can get SIP phone service for way cheap, and end up with more for less. Plus, if you do SIP, you don’t have to buy a PSTN interface card, which will save you hundreds of dollars.

SIP? DID? I have to research that. I thought the only way to use our current outside lines are with an interface card. I’ll have to weigh the advantages/disadvantages. You seem to indicate that straight SIP would be the most advantageous rather than to use an interface card. I’m not understanding how the existing outside line would come into the system without an interface card. I will research.


The existing lines would not be used, although, in the UK, and probably most countries with an active telecoms market, the phone numbers might still be usable.