For short call only, no different than it is now. (This actually started in 2000). As I said in my post, "Your FAA duty day starts at the beginning of the on call period." If you get called 4 hours into your on call period you are already 4 hours into a duty period and can only be given an assignment that takes this into account. This is current practice and will continue to be so except the new duty day limits will apply, still counting all time already on call before the assignment. The only change is the callout period is going from 15 hours to 14 hours with the min time off between callout periods going from 9 to 10 hours. LCAL has already implemented this. LUAL will implement it in January.
Long callout reserves are not in FAA rest and cannot be called out directly from reserve to an assignment without an intervening rest period. They are just telephone available 24 hours a day during their reserve periods. If called, they then go into FAR rest before reporting for the assignment. Contractually it will be 13 hours.
This is really no change from what we currently do. The big change came in 2000 when the FAA determined that their Whitlow Rule applied to reserves. Before then reserves were on short call 24 hours a day and treated as though they were in continuous rest, and could be short called at any time into a full duty day. This article summarizes the change that took place in 2000,
http://blog.aopa.org/flighttraining/?p=2327