"What is the best way to receive an IFR clearance when departing from a non-towered airport?" - Joe M.
“The first step is to consult the Chart Supplements (formerly known as the Airport Facility Directory (A/FD) for the airport.
If you’re using one of the tablet based applications such as Foreflight, the frequencies will be on the airport home page.
Procedures will be different depending upon the equipment installed at each airport. The communications section of the Supplement will list the radio frequencies and phone numbers available at each airport.
Many airports have a Remote Communications Outlet (RCO). This is a radio transceiver connected to an FSS or TRACON via landline. The pilot can request the clearance directly from the specialist over the radio.
Other airports may require the pilot to call the National Clearance Delivery Telephone Number (888-766-8267). This number will connect you with an AFSS specialist who can relay the clearance from the TRACON or Center.
Another good source is to call and check with the locals if you are not familiar with the airport. Call the FBO or local flight school and ask what method they use. Sometimes they know, for example, that even if there is no RCO, you can reach a nearby ATC Facility while still on the ground.
And you can always ask the last controller you were talking to before going into the airport. They usually know whether they may be reached on the ground or may suggest an alternate method of getting the clearance.”