2013 - a new 700 Mhz P25 trunked radio system began operations in the Boston area. Apparently this "overlay" system is intended to bring greater channel capacity to the pre-exisiting 800 Mhz TRS operated by the State. Systems details can be found at RadioReference.com (under MA State Police) and at Scan New England (again under Mass State Police - on the Massachusetts Wiki Page)
April 16, 2014 - at this time I suspect that the system does not have alot of active users. Perhaps some radio techs and higher level bosses have 700 mhz radios. There seems to be extensive patching between the 800 Mhz TRS and the 700 Mhz TRS. If you divide a 800 Mhz analog TG by 16 you will get its digital equivalent (ie Analog TG 45168 is the same as Digital TG 2823 - Boston Citywide 1)