Worldcall using opendns?

Ok I think worldcall's 203.81.204.23 dns server is forwarding requests to opendns' servers for resolution. You can confirm this buy doing an nslookup for a domain like bank.co.uk that is known to be unused:

nslookup bank.co.uk 203.81.204.23

Then view the ip you get in your browser and you'll end up at an opendns page. If you get 208.67.217.132 as the result then it'll end up at opendns.

Can someone else who has worldcall please confirm that they are using opendns?

yes nslookup also pointing to open dns servers.