I personally think of it as a very fancy electronic calling card that doesn’t require me to type in a long series of numbers. In fact, the integration with the iPhone is quite good and the call quality was pretty decent (in a test call to the UK).
All in all, this is an interesting alternative to Skype, especially if you can get free calls to other ChatTime users, without having to rely on the data network. I wonder how long ChatTime will offer free calls…