Phone Conference Call or Three Way Calling feature comes built in with many existing calling plans.  But until walked through once, you may not know how to use it.  Here is how it works. 

Almost all telephone calling plans today equip your phone with conference feature.  Such feature is more commonly described as "Three-Way" calling. It literally means you can have conversation with two other people on a single phone call.

Make a Call

First, you make a call to someone.

Put the First Caller on Hold

Second, you either press "Flash" button on your phone or quickly tap the switch hook of your phone. 

Make the Second Call

As soon as you hear a new dial tone, you dial another number. It's okay to dial while the first person is also on the line.

Connect the First Person

You're almost done here.  Now all you have to do is to invite back the first caller by either quickly tapping the switch hook or pressing the flash button if your phone comes equipped. 

Practice a Few Times

Most modern phones with cords come with a flash button.  Many cordless phones do not come equipped and this can get tricky. In this case, instead of tapping the switch hook, you must turn the "Talk" button off then on very quickly. This will take you a few times before you might get used to it.  

Don't Forget

In addition, always notify the first caller that you'd be putting the person on hold. While they're on hold, the call would be silent, and remind not to hang up the phone.