All of the medical helicopter services in this region can only be "dispatched" by personnel at their own dispatch facility.
CMC has 'flightwatch," which pages the helicopter personnel when they are either requested for a flight, or put on standby for a tentative flight. The actual page goes out on 462.925, mixed in with other medical-related paging. The details of the page are usually also broadcast on the Med Center Air primary VHF channel - 155.325 MHz / 91.5 Hz tone.
The LifeNet helicopters, out of Columbia and Orangeburg, are operated by AirMethods and dispatched from a large operations center in Colorado, They have two talkgroups on the Palmetto 800 system in S.C., and the Newport site seems to carry the 03888 talkgroup 24 / 7.
With both CMC and LifeNet, public safety agencies request the assistance of the helicopters by calling their respective dispatch centers via a toll-free phone number. The pilot of the helicopter has the final authority for accepting or rejecting a particular request, based on available weather information between the helicopter location and the landing zone, and other potential risks.
We do not have any civilian helicopters in our area that routinely fill the dual role of law enforcement and medical evacuation. The closest one in the Carolinas that I can think of would be the helo operated by the Dare County, N.C. sheriffs department.
Although Lancaster County EMS personnel have the CMC frequency in their radios, also listen to the county fire tac channels for air-to-ground communications with CMC helos around landing zones.
LifeNet will also generally use Lancaster County's VHF channels to communicate with LCFD and LCEMS units, although some county fire personnel have access to the Palmetto 800 system.