Asterisk phone systems is a software that uses a computer and turns it into a server for communications. A lot of multinational companies as well as small business utilize Asterisk such as call centers, government agencies, telecommunications carriers and even small businesses.
The program is for free and open-sourced, which is capable for lots of uses and makes older telephone systems obsolete. Since it is in fact a type of software, it can be manipulated and customized, thus adding to its versatility and function.