Robinpud - basically means that you use the phone line in your computer to make calls on. Cheaply. Or as LeahE says, totally free if you are both on it. Advancing all the time, defo where phones are headed.
We have it. Bloody cheap, easy to use and set up. Just log on to website and off you go. you´ll need a headset or handset. If you want to fork out, you can get a walk about phone which is much better unless your pc is in a good spot (ours in basement meaning I can´t see the kids in the garden, so tricky to use unless they are in bed). I think (if you are VERY techy) you can even get skype calls to your mobile. It really is amazing. If your family and friends have it, its totally free.
BUT - call quality can be bad. I think if your computer is relatively modern (ie less than a couple of years old) and your internet connection is good (ie not much crashing, taking ages to open stuff etc), you´ll be laughing - no different at all from a normal phone call. Ours for example didn´t work at all well on old pc (haven´t transferred it to new one yet, so don´t know if it will be any better now). You would be speaking and then the other person wouldn´t be able to hear you for maybe 15 secs, but you don´t realise they can´t hear you, so you finish your point and wait for an answer, and then have to repeat it, and then they will fade out when they answer, but not realise so you have to ask them to repeat themselves......It can be quite eventful. BUT my mum has it on her newish laptop and its clear as a bell, never fades out, so i think it´s just luck.
Will ask techie husband if there is anything else!!
All in all though, I would say its worth it.
HTH