Today's mail brought the SmartHome Spring 2005 Buyers Guide. Unless I missed it, there is no mention of Insteon in it. They do list a few UPB devices.
Lacking specific details on the SignaLinc RF device, I'm guessing (based on the fact that two are recommended in order to bridge the phases) they must send & receive PLC and also send & receive RF. If anything received as RF is repeated as PLC and anything received as PLC is repeated as RF, the phases will be coupled. There might be some confusion if there is any incidental PLC coupling of the phases - I understand that was a fatal flaw with CeBus.
I haven't seen any mention of Insteon RF remotes.