Since recalls do not replace attrition directly (attrits occcur on CA seats and recalls are brought into FODC9 and FO320 seats), the 75 recalls would be covering flying demand. At 55 block hours per pilot, that's about 4,100 block hours that will be flown by these recalls after they get through training. They would be partially covering movement out of these FO seats that are filling demand in the FO757 seat to fund ATL flying in 2007.
Naturally, the staffing dynamics are fairly complex since pilots are only qualified to fly one of the 16 flying positions in a given month and flying demand by equipment changes from month to month. Since it takes a couple months to get a recall fully trained and ready to fly, recall notices have to occur about 3 months prior to the flying month in which they are needed. These recalls have been in the plan for months; it was just recently that they were officially announced due to reaching the lead time deadline.
This whole staffing process is much more complicated that it may appear on its surface, and I'd be more than willing to answer any questions people have about it.