Here's another vote for CM15 X10 RF transmission.
As far as getting the signal across phases, X10 networks can use a phase coupler. Like this:
http://www.smarthomeusa.com/ShopByManuf ... tem/CR234/I've had several over the years. Trouble seems to be that anytime lightning strikes within ear shot, the stupid thing shorts out. Nothing else in my house has ever gotten knocked out by lightning, but the phase coupler goes every time.
This is my main reason for moving to Insteon. I'm hoping to eliminate the need for such a device with the PLM and another dual-band device talking via RF.