AIM 5-2-3 IFR Clearances Off Uncontrolled Airports
Chapter 5. Air Traffic Procedures · Section 2. Departure Procedures
A reference copy of the official AIM text for study. It is not legal advice or an FAA interpretation; always confirm against the current official source.
a. Pilots departing on an IFR flight plan should consult the Chart Supplement to determine the frequency or telephone number to use to contact clearance delivery. On initial contact, pilots should advise that the flight is IFR and state the departure and destination airports.
b. Air traffic facilities providing clearance delivery services via telephone will have their telephone number published in the Chart Supplement of that airport's entry. This same section may also contain a telephone number to use for cancellation of an IFR flight plan after landing.
c. Except in Alaska, pilots of MEDEVAC flights may obtain a clearance by calling 1-877-543-4733.