Most people learn their phone system on the job. The problem with taking a course on phone systems is that there’s so many phone systems out there. You’ll end up knowing how to use one system, and then go to your new job and have a brand new system that came out 2 weeks ago. But not to worry! Phones are not that hard to use. Generally, in a multi-line environment, you’ll have buttons for each line with lights indicating which lines are in use, or which line is ringing. It shouldn’t take long to pick up the basics, and you can always refer to a manual for the advanced features. Good luck.