The Times isn't going to put a full firewall up. Rather, it will permit access to a certain number of articles free, after which there will be a flat fee for full access.
Today's announcement is really more of a conceptual confirmation. Many details of the plan are forthcoming, including how much access will be free, what will be charged for full access, and what will be included in that full access. Executives even suggest that access may shift at times.
One thing that is clear: A print subscriber is automatically given full access.
The Times sees the move as a bet on the future of digital distribution and suggests it's time to find a stronger revenue stream out of it.