Echelon also has the "NES Data Concentrator" which looks like the ones in some of the pics sent by others. I have not spotted the one for my current apartment but where I was living, it was on a pole (easy to spot because of a bright blue LED) and looked like the Echelon version.
Also, I had found all of the different meters from various suppliers confusing but it is beginning to appear that most, if not all, are actually using LonTalk but referring to it by its ISO, ANSI or CE standard designation. Echelon's data concentrator also uses it. The meters and concentrators use Cenelec A Band (75-86kHz) or C Band (115-132kHz) for the powerline protocol and the signal amplitude varies, growing considerably stronger if it encounters "noise". The concentrator can be set to query the meter (for usage) on 5 minute to 24 hour intervals. There's an optional SO (?) pulse output which can be RS232C, a set of XYZ relay contacts or flashing LEDs. The pulse rate is 1 pulse = 1 Watt hour (i.e. 1000 pulses per 1kWh). A Zigbee module is also optional.
One affected user sees random ONs with an X10-made switch but not from a Smarthome Insteon/X10 module set to the same address and sees no valid X10 codes in an Ocelot log. Another sees randon ONs in one X10-made module but not in another X10-made module at the same address.
While Cenelec A or B frequencies can block (interfere with) X10, I think it may be high amplitude signals operating directly on the PIC processors used by X10 (although I'm unsure of the mechanism) that cause the random ONs. Power surges, spikes and brownouts can cause similar events.