Cheap asterisk card

What is a PBX ?

Why you need setup an ip pbx based on my cheap asterisk card ?

There are many asterisk card vendors, however, my asterisk card is cheap but good .

A PBX (Private Branch Exchange) is a switch station for telephone systems. It consists mainly of several branches of telephone systems and it switches connections to and from them, thereby linking phone lines.
Companies use a PBX for connecting all their internal phones to an external line. This way, they can lease only one line and have many people using it, with each one having a phone at the desk with different number. The number is not in the same format as a phone number though, as it depends on the internal numbering. Inside a PBX, you only need to dial three-digit or four-digit numbers to make a call to another phone in the network. We often refer to this number as an extension.
Most people are familiar with PBXs because they've used them in an office environment, but what if you wanted to use one in small office or your house? Enter Asterisk.
The beauty of Asterisk (see also Asterisk.org) is that it is free and offers all this functionality right out of the box. Asterisk is a software implementation of a hardware PBX and can run on a variety of hardware platforms. The features and benefits of owning an Asterisk PBX are numerous, and seemingly only limited by the imagination of the person who sets up and uses an Asterisk PBX.