May 2015 - 159.90 is the paging and response channel - a 'on scene' channel is assigned for each call - I have heard Ch3 and Ch5 assigned as 'on scene' channels - apparently the 'on scene' channels are used for unit to unit comms at the incident scene - incident commander to dispatcher comms are done on 159.90 apparently
December 2015 - units responding to EMS calls are told to use Channel 3 but all comms seem to come over Channel 1 - (or I should say - I can hear the dispatcher talking to units on Ch 1 (on scene, enroute to hosp, etc) - I dont know exactly what channel they are answering on) - I heard a fire call get assigned to Channel 5 - Radio Reference shows Ch 3 as a FG channel - they dont have any specific EMS channel listed