US and Canada 310 MHz as mentioned. 433.92 MHz for Europe. Much easier to get the correct stuff and if you use the 310MHz stuff. I believe it is not allowed legally overseas, by the country it is being used in.
The Powermid is on 418 MHZ and the new dual RF Icon Remote does both 310 MHz for X10 control and 418 MHz for a Powermid Receiver. Used to remotely control a entertainment device.
Most of my data comes from the FCC database of accepted devices. Search for X10s prefix B4S and you will find many devices. Some even with schematics.
Once you get the X10 signal on the power line it is 120 KHz no matter where in the world you are. Since it is timed to the power line the 50 Cycle contries signals take more time to be sent.
Where you talking X10 or Insteon over Smarthome?