fwiw... tmk… The only RF INSTEON products at the moment are the phase-coupling units.
That's explained a bit more in:
http://www.insteon.net/pdf/insteondetails.pdf Page 12 and 14 show how the different types of INSTEON devices communicate with each other.
I think their marketing materials make it easy to believe that the SwitchLinc Relays and Dimmers are RF, but they are only PL right now.
Eric