The New York Times will charge a subscription fee for frequent readers of its Web site and mobile applications starting March 28. It’s a gutsy experiment in resetting the financial equation of the newspaper industry.

The Times announced the move, expected since last fall, in a letter to readers by publisher Arthur Ochs Sulzberger, Jr. “On, you can view 20 articles each month at no charge (including slide shows, videos and other features),” he wrote. “After 20 articles, we will ask you to become a digital subscriber, with full access to our site.”

Its subscription plans start at $15 for four weeks of unlimited access to the Times site and its smartphone applications (for the iPhone and iPod touch, Android phones and BlackBerries). A $20 option replaces phone access with tablet access, in the form of the paper’s iPad app, its Times Reader 2.0 program for Windows, Mac and Linux computers and its NYTimes app for Google’s Chrome Web Store. A $35 “All Digital Access” plan covers all of those devices.

Print subscribers, even for Sunday-only delivery, get unlimited online and mobile access. So do subscribers to the International Herald Tribune.

But you can also duck under the Times' “paywall” by clicking links to Times stories on other sites. Under frequently asked questions, the Times notes that you can exceed that 20-article quota by following links to the Times from “Facebook, Twitter, search engines, blogs and social media.” You can also read up to five Times stories a day by clicking through Google search results.

(The FAQ also notes that the new price plans don’t cover Times subscriptions on Amazon’s Kindle, Barnes & Noble’s Nook and other e-book readers. Nor does it include access to the paper’s online crossword games.)

The 20-article limit applies to both the Times’ full-sized and mobile sites, and the subscriptions don’t remove ads from either sites or apps.

Will it work? It could: Newspaper-industry blogger Alan Mutter wrote on Monday that the Augusta Chronicle had implemented a paywall along the lines of the Times’ while still increasing its Web traffic. That’s a key factor in making this sort of plan successful: You need to keep people reading your site to be able to sell ads at a healthy price, even as you build this extra source of income.

(Disclaimer: I grew up reading the Times and remain a fan. I also happen to like newspapers and journalism in general.)

But the pricing here doesn’t quite add up. Why pay $35 for four weeks of All Digital Access when you can get that for free with a Sunday-only subscription, $15 for the same period of time? (3:54 p.m. Scratch that: Astute reader and fellow tech writer Glenn Fleishman noted that the $15 price is only good for the first 12 weeks. After that, you’d pay $30 for four weeks of Sunday delivery--still cheaper than All Digital Access at $35. Another computing scribe, Kirk McElhearn, wrote earlier today that the NYT’s Book Review subscription, at just $91 a year, also seems to qualify for free online and mobile-app access.)

The segregation of access by types of device also looks odd. How many people own an iPad but not a smartphone? It makes a little more sense to separate Web-only subscriptions from those that involve app access, however. The Times has to fork over 30 percent of iPhone and iPad app subscriptions to Apple if they’re purchased through its App Store, which I expect will be the easiest and most obvious way to pay in each program.

We’ll see soon enough. (Or today: The paywall is already up for Canadian readers.) You tell me: If the New York Times’ current offer doesn’t interest you, what sort of subscription offering would?