When describing Rebtel to people who don't know about it, I sometimes say it's like skypeOut, only not using your computer but instead using your mobile. In that way, most people can relate to it. Skype's free, when calling computer to computer, but calling with skypeOut (to fixed and mobile phones) cost money. I've taken some time checking these rates and comparing them to Rebtel's rates.
Although skype's using the computer, the rates are often cheaper with Rebtel. Incroyable!
Here are some extracted rates from skype and Rebtel to mobiles:
These were taken randomly from both rate sites. The differences are not big, but concidering that calling from skype means having to call from your computer with a headset, compared to being mobile, it's pretty different!