Part of it can be that, yes, and you can somewhat confirm it by taking note of whether or not your phone constantly has fewer bars of reception. But what affect

Part of it can be that, yes, and you can somewhat confirm it by taking note of whether or not your phone constantly has fewer bars of reception. But what affects this more are domestic cellular grid configurations telling phones how often they should announce their presence to base stations. With the advent of 3G the beacon rate of handsets in the grid is vastly higher than during the 2G era. What you're noticing is that your phone is "checking in" with the grid - turning its transmitter portion on and letting the grid know it's online and available - a lot more often than back home. As another datapoint to this I've visited Malta several times the past 3 years, and on every visit I notice that my phone (compared to in Sweden) drains notably less battery.