This is for people who don't want to pay a dime for phone calls to any phone (mobile or landline), and who can have a PC with an Internet connection... and who wouldn't mind half a minute of advertising. Tuitalk offers you a number of minutes of completely free call per day if you watch an ad for them. The calls are possible to 40 countries, with varying call lengths allowed for a day. For some destinations, you can have as many as 18 free minutes for a day, spread over 3 calls.
It works like this. You register with Tuitalk, then you download and install their application on your computer or your mobile phone. To make your call, dial the number and watch the ad (or rather wait for it to finish). Then you can talk. Here is the list of countries covered and the amount of minutes offered.
I know what's in your mind now. Where's the trap? I don't know if there is any, and there doesn't seem to be any. We can eliminate suspicion thinking that they make good for the free calls given away by earning advertising revenue - they act like billboards, and you are the audience they offer to advertisers. This said, I would emit a reserve on the application you have to download and install. I hope it has no adware or spyware attached to it. I have the feeling there isn't any. But it's only a feeling. If you know anything, let us know.