From VTwiki

What is 3-Way Calling?

Using 3-Way Calling, you can have a phone conversation with two people at the same time. All three people can talk at once. To set up a call, just call the first person as normal. Once they have answered, press the flash button, and dial the second person. Once they answer, press the flash button one last time, and all three parties will be connected.

How to Expand 3-Way Calling Using 2-Line Phone System

It has been confirmed that users who have 2-line phone systems with the conference feature can utilize the ViaTalk's second phone line to place 5-way calls.  "How to Have a Five-way Phone Call." Nov 11, 2007