Stand Alone System
Building your own phone system is fairly easy to do. If you've ever loaded an operating system, like Windows, on a PC, you may be able to do this yourself.
You can use just about any small PC, such as the popular integrated systems available from Intel, Asus, Dell, etc. Note that you should try to find a system with a bootable CD or DVD drive, for loading software. Otherwise, you can use a bootable USB drive, but it is slightly trickier.
You'll need to download and install the FreePBX software, available HERE. The PBX software is bundled with the Linux operating system, on a single .iso image file. So installation is fairly easy. You'll just need to burn the image to a CD, DVD, or USB disk, then install on your system.
Once your PBX is up and running, open a Support Ticket and request the "Trunk Walkthrough". We'll send you step by step instructions for a basic setup.
If you prefer a Windows environment, there are several PBX software options available.
3CX is the most popular and has a free (limited feature) version availalable, as well as commercial editions starting around $500.
TekIVR by KaplanSoft is also worth a look, if you just want something very basic, and is priced around $150.