Some things above aren't really true so to clarify (this is from a technical POV):
2G:
General characteristics are coverage stays the same no matter what, calls/data limited to "slots" on a cell site, encryption is good but not great (nothing to worry about from your pov).
Data is limited to GPRS speeds, averages at about 30kbps
Calls are either Full Rate or Half Rate. Half Rate sounds terrible but works in high density areas (think concerts, high pop attractions, sites that have extreme density sways like convent garden) and uses just over half the rate of a full call allowing us to pack more simultaneous calls into one site.
EDGE:
General Characteristic is that it's 2G based but sort of overclocked. Data is low latancy compared to GPRS and can sometimes beat 3G in newer variants.
Data speeds around 100kbps, can be higher but depends on other factors.
3G:
General characteristic is cell sites can suffer shrinkage due to over-population, signal does not go as far (power depending) as 2G. More simultaneous connections possible due to the way it works, security is stronger than 2G.
Calls in general are better on 3G due to the codec used (Adaptive Multi Rate). Orange support "HD" calls as long as phones both support "Wideband Adaptive Multi Rate" then you'll get "HD" calls which are double or higher in terms of bandwidth and therefore, quality.
Data comes in standard 3G, HSxPA and HSPA+ speeds which vary from 0.5Mbit to 7Mbit (useable, the specs are hilariously untrue perfect scenarios).
Modern 3G chipsets don't use that much more power than 2G, this is an old myth.