While it is a bit early to give this fresh new site a close examination, I gave it a play via my favoured Maxthon browser.
First of all Zootok gives two free calls, so messing around will cost you nothing. Joining involves filling in a very small form. This maps your email to one designated phone number. OpenId has been promised in the future.
I think calls are 50p (it's hardly mentioned), which is not bad for anywhere in the world for an hour. This may get competition in the long run. My credits were used even though I didn't connect - though the site promises otherwise. Probably a service issue.
After you log in, there is a nice user page that gives you a "phonebox", reminds you of your designated number and a click to get more credits from google checkout. You can just connect another number directly to your designated number via the phonebox, or do the same thing via a text message to Zootok's number.
There is a very rudimentary address book, though only for mobile users. A good idea that will be a nice feature for the future. The terms"contacts", "names", "shortcuts" and "alias" all get used on the same page- maybe indicating that the designers lacked a critical eye at times.
There are no nice error pages or reports as yet. Putting a bad number into the phonebox (I accidentally tried an alias) gives back an HTTP 500. Logging in with the wrong credentials gives fair warning but unfortunately the message is in the same black colour as the rest of the text; hence you may not notice it.
Most of the new web building frameworks seem to support good REST type urls, and Zootok is easy to get around because of it. When routing and redirection is well managed, this gives any site a well organised feeling. In Zootok the credit account site and history site are situated off your user page url and all look logical. I can see that I am user "12", which I don't really need to know - I'd prefer to be user "DE". Attempts to "jump the fence" and visit user 13's page are correctly ignored.
The contact entry page is basic, and does not encourage people to put in comments, wishes etc. There is no blog associated with the site yet either. Given that the term "zootok" has no other meaning, the designers have complete control of their domain.
All in all this early offering seems promising - and hopefully will be polished in the near future. It also should spur on other developers to pitch in with their own efforts.