Here’s a thought concerning mobile power consumption in UMTS networks: In the uplink transmission direction, the power required to send data to the network depends on the amount of noise present in the channel. The more noise, i.e. the more other users are transmitting data to the cell at the same time, the higher the required power to send your data. That means that if there is a lot of activity from other people in the neighborhood, your own battery consumption increases when you transfer data yourself. That doesn’t necessarily mean this has a significant impact on autonomy time but it should be measurable. Also, it should be taken into account that other factors have a similar or even bigger impact on uplink power requirements, e.g. if coverage is weak at the location where a mobile device is most of the time. But the idea remains: It’s not only you that decides how much power your device uses for communicating with the network.