Ok I think worldcall's 22.214.171.124 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 126.96.36.199
Then view the ip you get in your browser and you'll end up at an opendns page. If you get 188.8.131.52 as the result then it'll end up at opendns.
Can someone else who has worldcall please confirm that they are using opendns?