Not sure about Ambient but here is what Echelon is doing on the gas/water side.
"As part of this deployment, the NES System will also be used to communicate to approximately 25,000 gas meters via a Meter-Bus (M-Bus) interface, a European standard for connecting various consumption meters such as heat, water, and gas meters. Using the newest members of Echelon's second generation NES electricity meter family, which can act as an "M-Bus master" for up to four attached M-Bus devices, these gas meters will be able to report alarms and be read over the NES network on a fixed schedule or on demand, and the usage can be profiled over time. For grid operators, like Nuon, that serve both gas and electricity customers, the ability to read the gas meters over the same infrastructure being deployed for the electricity meters can bring significant cost savings and service improvements."
rightofway: I believe what they are saying is that the network is capable of communicating with the gas meters; however the communication units in the gas meters are not Echelon. There is no power available near water or gas meters so there is no opportunity to place PLC in a water or gas meter application. In the application referenced, it appears that the gas meter AMR unit utilizes the Lonworks protocol so it can communicate with NES, but it does not utilize PLC
The radio for gas and water meter applications must be extremely low power because it must survive on battery power for years. It is also wireless because there are simply no wires at the water or gas meter. As far as I know, Echelon has no low power wireless technology. As such, they cannot generate much hardware revenue from water or gas meter sales. At best, they might be able to sell a processor chip into the AMR unit but my guess is that the power consumption of their chip is too high for these applications.
Itron actually sells both the meter and the AMR units.