There are already some services like that appearing, one that i know of consolidated status updates from FB, twitter, orkut et al.
but no one is tackling the basics. One of the basic services required is a universal directory service. In Windows world, Active Directory or AD plays that role.
on web world, there has to be a centralised database, which stores all this information.
implementation will not be that difficult. the Online Directory will basically pull in information from whereever you have an account, so if ur on FB, it pull in info from their. and then provide info to whoevery needs it and is authorised to get it. today for a lot of things Google Accounts is playing that role.
the biggest advantage will be that you need to provide info only once, and edit it only at one place if something changes. the push mechanism of the OD will update it everywhere else.
the challenge is, how to ensure that everyone has just one account. well...do you need to ensure that. but even if their isin't a single account for everyone, but am sure from a 'we wanna catch the paedophiles' point of view, all accounts should have some kinda linking.
anyways, so the OD not only provides information, but is also searchable. So i need to search for a person, go to the OD and know that they exist, and that they are a specialist in hair care adivsories...and their public number is given....
and this service is something free of cost which sits on ur 'interface to a space' desktop, and can be use as one of the default services u can use.