3G is not widely available in India yet and just few percent of users actually use 3G service. But most of the new mobile handsets available in market are equipped with 3G, those handsets by default kept in dual mode settings (factory settings). Dual mode automatically switches between 3G/UMTS or 2G/GSM network according to availability. If phone is set for dual mode, it will continuously search for an available 3G network and this will consume some battery power. Also 3G consume more battery than 2G network does. So those people who don’t use or not using 3G service for that moment can save some battery power by turning 3G reception off in their handsets. Most of those handset users are not aware of such settings.
Nokia users can change network mode from Settings > Phone > Network > Network Mode.
People using other brands mobile can find this setting somewhere under Network settings.