More info about VoIP Number ?

I have been immersing myself in VoIP Drupal and coming to the conclusion that I may not be fully grasping the power of this package.

Could someone give me a concrete idea about what VoIP Number, as a CCK field, can do? I understand in general that it can store numbers, but what does that mean in practice? Is this a way for, for example, linking VoIP to CiviCRM for surveys, and/or is it possible to do other things with it?

Thanks in advance for thoughts, answers, or other feedback.