Asterisk is a flexible, scalable, inexpensive PBX system that runs on Linux based PCs. We've been using Linux for several years (and various UNIX systems for at least a decade before that), so when we came to upgrade our own telephone system, Asterisk seemed to be the obvious choice.

We now use almost all of Asterisk's capabilities in-house to some extent, and we can help you take control of your own telecommunications in a way that is difficult with most traditional telecommunications providers.

Why is Asterisk different ? Well, it's a software-based PBX, it's Open Source, and it uses off-the-shelf PCs together with inexpensive telephony hardware manufactured by Digium.

Because it's based on Open Source software (both Asterisk itself, and the underlying operating system), and because it handles a variety of hardware, there's no vendor tie-in, and support is both responsive and cost-effective. In fact, if you have a UNIX-aware IT department you may well be able to do it yourself.

You can use Asterisk with PSTN, Basic Rate ISDN (ISDN2e), or E1 (ISDN30) connections from any carrier. It also supports the SIP and IAX2 Voice over IP protocols which allow VoIP communications between remote Asterisk servers and low-cost Voip providers.

Within the organisation, Asterisk provides all of the facilities you'd expect from a modern PBX or call centre system (including voicemail, music-on-hold, agent login, call recording &c) and it supports IP phones so that you can either plug phones into the same network cables that you use for your PCs, or run softphones with headsets on the PCs themselves.

Is there a downside ? Well, there are some pitfalls, but they're all avoidable.

Hardware that connects an Asterisk PBX to a UK PSTN (analogue) line will not handle UK Calling Line Identification (CLI). This problem can be overcome by the addition of an external gizmo, but that's not very elegant, is it ?

Because Asterisk is a software PBX a lot of the overhead that would traditionally be handled by more expensive, proprietary, hardware is now handled by the program. In particular, Digium's telephony hardware imposes a high interrupt load on the PC, and some motherboard PCI bus implementations don't handle this too well.

Of course, if we help you to implement an Asterisk switch (or call-centre environment) then these are our problems, not yours.