The only way that this would work is if people were silly enough to singup with a service like this.
seriously, would you setup to a service who did this?
there are plenty of well known companies out there doing VoIP and PLENTY of free applications which people use. SKYPE being just one.
yes, this could happen. but so can they get it just as easily by going through your trash or calling you on your mobile pretending to be someone from your bank.
its called social engineering; because it relies on the victim falling for whatever the 'hacker' is doing.