The 319 shuttle entered service on 10/1/00 and are exclusive to BOS, meaning the 9 A319's which will be configured in Shuttle layout will be flying the BOS-DCA, and BOS-IAD routes only.
The first 4 A319's were delivered in September and the 5 remaining on order will be delivered by the end of the month. Ships 750, 751, and 752 are currently in service.
The 733 Shuttles are being refurbished with 2 class cabin at TPA and will enter mainline service as the mods are completed.
Having the 319/320 for the Shuttle allows a US 32X Shuttle pilot to fly either type, something previously not possible with the mix of 733 and 320.