47 CFR 87.217 - Frequencies.
(a) Only one unicom frequency will be assigned at any one airport. Applicants must request a particular frequency, which will be taken into consideration when the assignment is made. The frequencies assignable to unicoms are:
(1) 122.950 MHz at airports which have a full-time control tower or full-time FAA flight service station.
(2) 122.700, 122.725, 122.800, 122.975, 123.000, 123.050 or 123.075 MHz at all other airports.
(b) 121.500 MHz: emergency and distress only.