I believe a majority of them are already deployed internationally. The thing is, given their range, these aircraft will not utilize an entire 24hour time cycle in the air on their *relatively* short trips to Europe (side-trips to Goose-Bay notwithstanding).

I'm not entirely certain, but flights like IAH-AMS/EZE block out at almost 24 hours for a gate-to-gate roundtrip (including ground time). I would not be surprised to learn that specific aircraft are dedicated to these routes, and would thus not rotate through the route network.

OTOH, the 757-200s have enough dead-time when they get back to a hub to be sent out on shuttle missions to places like FLL & MSY. I don't think that 757-200s will be a complete rarity on domestic flights, but will simply be confined to certain routes.