The disadvantages of Asterisk

There are, however, some disadvantages in choosing Asterisk instead of a proprietary solution.

Familiarity with Linux is required
Asterisk works best under Linux. This means that you will need to know how to install, configure, and maintain a Linux distribution. Since most of the work in Linux is still done using shell commands, you will need to be comfortable working with the shell.

You will need to learn the Asterisk dialplan
The Asterisk dialplan is a form of scripting language specific to Asterisk and one of the primary ways of instructing Asterisk on how to behave. You will need to learn how to write a dialplan and what contexts, extensions, and priorities are.

No user friendly interface
By default, Asterisk doesn’t feature a GUI. There are some GUI solutions (like Elastix and FreePBX), but most of your work will be done through a CLI.