When Facebook launched its API platform earlier this year, the social network platform took off. By giving developers the ability to build their own applications that could be embedded within the social network, Facebook seemed to have found a a bit of gold. With a built-in audience, developers flocked to the platform. Users loved the new apps, especially how nicely they were integrated with the platform. And Facebook pulled in millions of new users and generated oodles of page views, all of which lead to talks with Microsoft, Google, Yahoo and others that have seemingly valued the company at a whopping $15 billion.

This week, MySpace followed suit, announcing at the Web 2.0 Summit in San Francisco plans to open its platform up to third-party developers as well. From blog Read/Write Web, here’s what MySpace has planned:

1) In the coming weeks MySpace is launching a catalogue of all widgets and tools available on MySpace;

2) In “several months” they will make industry standard APIs available through a new platform where developers can try new things in a sandbox environment;

3) MySpace users will have the opportunity to participate in an opt-in beta test program, to determine usability;

4) Users will vote and ultimately determine which of the third party widgets get tightly integrated into MySpace;

5) MySpace will formally introduce the best widgets into the community, with what they term “highly developed integration”.

This is a bit different than Facebook’s “wild-west” third-party-app approach. With an audience used to voting (via “friending”), the MySpace strategy just might offer the right mix of openness and control, a concept with which Apple is wrestling right now in allowing third-party apps on the iPhone.

The “API wars,” however, call into question what “open” *really* means in the context of a social network. Is it just the ability for outsiders to add applications?

No. What is more important to end users and third-party developers — and what is really the social net owners crown jewel — is the “social graph” of connections between all the users on the site. A social graph goes beyond individual customer record or profile information to mapping the connections an individual user has — and not just the first degree, but several degrees deep.

In telephony parlance, if call detail records are an equivalent of a Web site user profile and the cookie tracking what an individual user does, than the social graph takes those records into “3-D” –essentially tracking a user’s extended universe of connections and seeing connections between multiple levels of users.

That, in a nutshell is what makes social networks so powerful.

So what does it mean to “open up” the social graph? It includes:

1) Providing individual users the ability to take their social data with them to other sites and applications

2) It provides third-party sites and developers with access to that data to leverage it in their own applications

3) It ostensibly would allow synching of social graph data between multiple sites, significantly lessening the “entry fatigue” of having to re-enter data at multiple sites

You’ll notice that in its plans to “open up,” MySpace, the world’s biggest social network, doesn’t mention sharing its users graph of social connections. Facebook, which has grown like wildfire this year and has the biggest share of attention in the social network market, has started talking about sharing its social data soon. Facebook CEO Mark Zuckerberg said at Web 2.0: “It’s the users’ data. We want to [make it portable.] That’s the goal.” But he declined to give a time frame. Meanwhile, Google is rumored to be announcing its social network plans in early November. Given its huge advertising lead, and relative trailing effort in the social network area (its Orkut social net is a bust in the U.S., big in some overseas locales) to talk a lot about more open social network environments. Basically, it “wants in” to what Facebook and MySpace already own.

Do telecom service providers own anything equivalent to a social network’s social graph? At first thought, we’d say no, though as hinted at above call detail records are information-rich and enable telcos to track (and bill) for small actions at an individual level.

How service providers deal with the power of the Web social graph is a key competitive question moving forward.