If you 1) want to test the ringer on your home telephone, 2) use the phone as an intercom so you can talk to someone else in the house using 2 extensions, or 3) prank call someone you live with, you need to get your own phone to ring. Dialing your own phone number doesn't work; you get a busy signal because you are already on the phone.
Call your phone company and request the ring back number for your phone. Most phone companies, in different areas, have a 2 or 3 digit code they can give you to use to make your own phone ring.
Follow the directions of your phone company for using the ring back number. In many areas, you need to pick up the receiver of the phone, dial the code that they gave you, then hang the phone back up for a second.
Pick the receiver back up off of the phone and listen for tone. The tone is typically a low frequency tone and may be broken.
Enter your phone number into the phone, or the last 4 digits of your phone number. This varies depending on where you live, your phone company can tell you which one to use.
Hang up the receiver on the phone and wait for it to ring.
Some phone companies have added a low tone to the line when you answer after ringing your own phone. This is to discourage customers from using the phone ring back number frequently to make their phone work like an intercom. You can still hear the person on the other phone extension, but the tone is also present.