I haven't had time to look at ZooTok inside out but I registered, and it worked. You can make calls from the site or via an SMS. Lets take a look at the basics.
1) The first call is free - of course it is. Otherwise you wouldn't use it would you?
2) The site is simple to use, with simple url names.
3) I can make top ups, check my call history, and check my details in one click
I'll make a more detailed examination later.