Facebook said last week that they aim to be the next Mobile Address Book. Just like the address book on my Blackberry connects with Yahoo’s corporate LDAP servers to look up the latest phone number or email of any Yahoo employee, Facebook and other social networks are building mobile clients to become the consumer version of the Blackberry Enterprise Server.

Connecting on Facebook is easy – invitations come in, you approve them, and then you each get access to more information about that person. The first time I installed the mobile Facebook app on my portable broadband device (Blackberry, not iPhone) was when I needed to look up a phone number on the way to a meeting with Mary Hodder. We had set the whole thing up on Facebook and it never occured to me as I walked out the door that I didn’t have her phone number. I downloaded the client and installed it while walking over to meet her so I could confirm that address which wasn’t in my phone’s address book.

The concept of a connected address book really takes hold in the mobile space when it’s a pain to navigate the web to look someone up. Yahoo has their oneConnect client for the iPhone. LinkedIn and Plaxo also have mobile interfaces.

So who is going to build the most compelling mobile address book? What are the most important elements?

  • When someone updates their profile, push updates out to each address book.
  • Lookup service to find contacts not in your address book
  • Import and Export of contacts.
  • Avatar or Photo support as a visual memory.
  • Fields for profiles on other social networking sites (MyBlogLog, Twitter, Brightkite, Last.FM, etc).
  • Lifestreaming to browse your contact’s latest updates. Nice to know before you call them, gives you context.

Yahoo, Facebook, LinkedIn, Plaxo, or something else? Which service will pull together all the features you need and gain the critical mass needed to become the default address book in the cloud and on your phone?

Update: Some great additional features listed in a Computerworld article by Mike Elgan;

  • When a contact calls, your phone displays a photo, social networking “status” info, as well as past meetings and any notes you’ve entered on that contact.
  • Choose your own written form of communication: e-mail, social network message, IM, Twitter, SkypeChat — whatever. So, for example, you can choose e-mail, and I can choose Facebook messaging. You send an e-mail to me, and I get a Facebook message. I reply with a Facebook message, and you get an e-mail.
  • Connect with calendar data so meetings with contacts are logged with the contact data. That way you’ll be reminded in the future about your history with each contact.
  • Kill any contact information. You should have the ability to decide you don’t want to share your Skype contact anymore, so you should be able to blast it from everybody’s address books.

Found these via a new aggregate news feed on Mobile Social Networking.