It seems like we're at the start of a great experiment to find what types of digital content people will pay for. The Web has been in love with The Cult of Free to the point where it's threatening the producers of content with extinction. There simply isn't enough advertising money to support everything. So what's next? The trick for content providers is to create tiers of content with value enough to get people to pay up. It's going to be tough. Mobile appears to be the first front. The Wall Street Journal this week flipped the switch on charging for much of the content available via its iPhone and Blackberry apps. Check out the reaction from those using the app -- 1000 of its 1500 ratings are one star with most are vowing to never use it again. (http://www.wsj.com/iphoneinstall)The newest test: Someecards. It rolled out an iPhone app today that costs a modest 99 cents. It's less than the cost of a Coke. It'll still be interesting to see if people take to these kind of microtransactions for content as a behavior. It would be unheard of to ask for 99 cents to use Someecards.com. But it might just work in mobile. There's quite a bit on the line. As Fred Wilson recently pointed out, "We need a scalable business model for mobile web apps. Display advertising is not likely to be that answer."