Tonight sees the official launch of Facebook Connect for iPhone, with social games publisher Playfish launching its Who Has The Biggest Brain? game on the App Store to tie in with the launch.

We talked to CEO Kristian Segerstrale to get the full lowdown on the company's plans.

"We're a launch partner for Facebook Connect, and one or two others are tweaking their games to use it," he says. "Who Has The Biggest Brain? is out this weekend, and two of our other games, Word Challenge and Geo Challenge, will be out by the summer."

The big deal about Facebook Connect is that it lets players sign in to games using their Facebook logins, and then compete against (or collaborate with) their friends, while also publishing their achievements to their profile news feed.

For existing social games on Facebook like WWTBB?, it allows them to launch spin-off iPhone versions that are fully integrated with the original.

"It's revolutionary for the mobile games industry," says Segerstrale, who left his previous job as EMEA boss of Glu Mobile to set up Playfish.

"This announcement enables us as a business and as an industry to start creating games where the emotional reason to play is to interact with friends, rather than designing games around this proverbial 'waiting for the bus' moment. And while people think of social gaming as being stuff people play on Facebook, this is the first time that what's previously been pure social games has expanded into the broader games industry."

There's plenty of questions to get our teeth into though, starting with the business model. WWTBB? is being sold for £2.99 in the UK App Store, whereas on Facebook the game is free to play (albeit with a paid for 'Pro' version - which is the one that's been converted to iPhone.

However, much of Playfish's revenues on Facebook come from advertising or micro-transactions. Although ads are possible in iPhone games, micropayments aren't (yet). How does Playfish see this side of iPhone gaming panning out?

Segerstrale chooses his words carefully. "The version that is live this weekend is a premium product, but in the broader scheme of things, we are huge fans of the free-to-play model with micro-transactions. Operating these kinds of games, where they're more like services, over time becomes a little bit incompatible with a pay-up-front model. So we're very much looking forward to innovations in billing on the iPhone and other connected platforms."

What about issues when the iPhone game is fully compatible with the Facebook version? Is it fair to have someone using a touchscreen iPhone competing with someone using a mouse for the Facebook version? Segerstrale says that Playfish has put a lot of thought into the balancing required to make it fair.

"Our designs across the board are pretty touchscreen-friendly, as we thought about this a lot when we first started developing our products," he says. "We spend a lot of time balancing, as we are trying to make these mobile versions extensions of the core game experience."

He admits, though, that some players may be able to get better scores on iPhone than on their PCs. "Well, if you're a piano virtuoso and you spend time practising your multi-finger techniques," he laughs.

How about updates? On Facebook, Playfish and its social games rivals can constantly improve and tweak their games, safe in the knowledge that they'll be generating constant revenues from ads and micro-payments. Doesn't that pay-up-front model hamper this approach on iPhone?

"We will work very closely to listen to our players and roll out features as time goes along," says Segerstrale, who is keen to stress that regular updates will be key to keeping WHTBB?'s players engaged on iPhone.

"But yes, ultimately for a service model to make sense on the iPhone, the business model has to follow suit," he continues. "For games where the main feature is rewards around updates, the business models probably need to evolve towards more subscriptions, micro-transactions and advertising."

Playfish doesn't just make games for Facebook, of course - it's released some of its games for MySpace, Bebo and Yahoo too. What about letting players sign into its iPhone games using these logins rather than Facebook? Segerstrale says that as they bring out equivalent technologies - for example MySpaceID - Playfish will be interested in working with those too.

Unsurprisingly, Segerstrale thinks social games are going to be big on iPhone. But what about rival publishers from the traditional console or mobile game industries? If Gameloft and EA Mobile get to grips with Facebook Connect quickly, can't it be as powerful for them?

"Ultimately, in order to make playing with friends meaningful in any game, it does need to be designed to play together," he says.

"So the people who will derive most advantage from Facebook Connect are the people who design their games in order to be played together. So I'd expect more titles to migrate from social networks to iPhone using it than traditional mobile games."

Really? You'd have to assume that the console and mobile firms will quickly catch on, surely?

"We've seen a whole bunch of games trying to make the leap onto Facebook [from mobile] relatively unsuccessfully, because they weren't designed for people to play with each other," says Segerstrale.

"The games industry is changing, though, and social gameplay will have a large impact. Every game designer and developer should be thinking about it, but it's a fundamental shift in how you think about design. It's not something you can do with just a quick port."

One last question, then, about money. How big an impact will iPhone have on Playfish's revenues, and how soon? And while he plays a straight bat, he does have some information on how the company is doing on existing platforms.

"We've build some of the more successful properties on Facebook so far, we've raised a certain amount of venture capital, and we are profitable, so we are pleased with our financial performance from that perspective," he says.

"But it's too early to think about this industry in terms of revenue. It's about a broader watershed in the games industry, so it's about understanding how consumers play these games and what they value. It's fundamentally a nascent industry, but we're in the very early days of something we believe will be very large. And iPhone fits right into that."