Social networks, up until now, have been at the center of so-called data portability efforts — new ways for developers to let you connect with friends across web applications. Companies like Facebook, MySpace and Google have introduced ways for you to access your “social graph” on other sites, letting you do things like see which friends also use the site.

But there are big missing pieces of social data and they’re on your phone — your address book of numbers, who calls you, and who you call the most. Skydeck, a startup that lets you aggregate and analyze your phone calling behavior based on bills from your phone carrier, is introducing a way to see the strength of your friendships, and your connections to friends of friends. See screenshot, above. Signal bars show you the strength of connections based on call volume, frequency, and number of mutual calls. The company is also announcing new application programming interfaces for developers to build their applications using this data.

A developer could build a Facebook application that matched your Facebook friends with Skydeck data showing which of them you talked to the most, and how much you talked to each person. Or maybe a developer could build a desktop application that shows you a meter with how many cell phone minutes and text messages you have left on your monthly plan. For business users, Skydeck data could be imported into Outlook and cross-referenced with your email contacts to show you who you both talk and email to the most.

Skydeck chief executive Jason Devitt claims this is the easiest access developers have ever gotten to phone usage data, with the API being based on the OAuth protocol for connecting APIs. As we’ve covered, Skydeck is going up against mobile carriers that until recently have shown a certain antipathy towards third parties, giving only a select few other companies access to their users, and even then at a price.