In case anyone else is ever looking for info re- US Flight Following, the following references should be of use:
Flight Following - A SafeAir1 Safety Series Article by Tony Munday:
http://www.vansairforce.net/articles...tFollowing.pdf
"The Why's and Hows of VFR Flight Following" - an AvWeb article by David Sampson:
http://www.avweb.com/news/avtraining/183268-1.html
A direct quote from the second of these directly answers my question:
To request flight following services, you first need to know the appropriate ATC frequency. If you're departing from an airport with an operating control tower, you can ask the tower for the correct frequency to use. At a non-towered airport, you can sometimes contact Flight Service and ask them for the frequency. Alternatively, you can look up your departure airport in the Airport Facility Directory (AFD) or other airport directory, look in the communications section, and find the frequency of the approach-departure control or ARTCC serving that airport. ARTCC sector frequencies also appear on IFR enroute charts. In any case, you should have the appropriate ATC frequency available before you take off.
Andy