From what I can deduce it looks like the idea of 2G only is due to battery life? If that is the case I would recommend you not to bother. 2G vs 3G is not the major battery change, and in some cases 3G can even have better results on battery life.
To double or triple a phone's battery life rather consider disabling data. Typically when you see an "G","E","3G" or "H+" in the top bar it means that the phone has an open pipe to the network which it needs to maintain. I have not used WiFi extensively myself so I can't comment on its power needs, but I suspect that only disabling mobile data and keeping WiFi on will not show any major gain.
That said, if you are going to disable data it begs the question why a smartphone? There are also some apps which tries to optimise the power usage requirements by disabling data connections when the phone's screen is off, and activating it periodically to allow applications to poll for WhatsApp messages, Email etc. It does mean that a WhatsApp may only arrive 15 or 30 minutes after it was sent but I have seen quite a nice improvement on battery when I used it.
These days I am happy if I make the day and charge every evening. Maybe a side note - one of my old phones (HTC Hero) at home can survive a week+ on "Airplane" mode and occasional movie watching to give an indication of how much power goes to the radio side of things vs keeping the phone running.
