The link below is overly technical but 2G is the GSM specification intended for providing mobile communication for voice,
and 3G is the specification for mobile communication with enhanced capabilities for mobile users other than voice. eg video calling, internet browsing etc

http://www.differencebetween.com/dif...3g-technology/

a 3G phone may well be constantly updating its location using GPS or checking for new email etc.. which all drains the battery.

theres no free lunch Snoopy