When you register a domain name and buy whois protection from your registrar it's important to remember that not all TLDs (top level domains) allow the registrant to hide his info behind such a service.
Registries that don't allow you to hide your information from the public:
Some registrars (such as Name) will warn you about this. Others, like Namecheap for example, will happily let you buy their whoisguard service, but you won't be able to apply it to your domain. Always check the rules when buying domains in a TLD you are not familiar with.