There are various web services like Plaxo that help you to organize your contacts. These web services will allow you to import, export and maintain your contacts. They also allow interoperability/sync-up across various Email clients or Address Book softwares. But I doubt whether you have some service by which you can share your phonebook across multiple phones.
It would be a nice service to build up so that you can keep your phones books in sync if you use multiple phones. And in this time I see multiple phones is not a remote possibility. For instance I have a mobile phone and a LG Wireless phone (for landline). Both of these phones support PhoneBook feature. But there is no interoperability between these phones. So I will not see my contacts in one phone in another.
As a first cut thought, the phonebook contact should have a standard industry agreed format. All the phones should support that format. Then build a common service which can be accessed by any phone service provider. Keep your phonebook in your phone in sync with your account in the server.