That site is years out of date, as these numbers stopped being inclusive on any networks a long time ago, and the provider uses other methods nowadays, including short code prefixes - see their Yourcallworld or Dialacode sites
When I post information, it's normally been tried & tested thoroughly by myself personally; along with all background information including the network calling the service, please try not to insult my intelligence as you'll only look like a fool.
This "is not" one of those old 07744/07755 sites that you mention, of which I'm fully aware, the domain has only been registered the end of Jan this year, I believe this is a recent service/certain 07755 range of numbers put into use, otherwise I wouldn't have posted.
If you care to look at the example bill, it has a bill date of end of Aug 13. It's been tested recently from the One Plan with a Zero charge usage cap & goes through fine without any out of bundles charges, please do explain yourself?
Despite what the Three price guide(s) show & how you read it, which I had previously looked at I've seen no charges, the same can be said for Pre-dial 07893 top-up numbers.
Andy, I suggest you do your homework first, before passing a casual comment about matters as it's not constructive.
Again this service is to be used from "Three Only" as you will be charged on other networks, it's seems inclusive at moment though this could change at anytime, so if using do keep an eye on your out of bundle costs to be sure.
It could be that it may only be inclusive on old plans pre 18 March 2014 or The One Plan, until someone tries a new plan we can't say for certain.