I think on the 3g as an example, if it is on 3G, then it will try to stay there and indeed, it probably CAN get the signal better than the 2G signal in many areas since the 2g build out pretty much has stopped. So, it won't make the jump to 2G unless it really cannot find a signal. But, we know that the 2g signal works better indoors, up high and in difficult areas. So, one can switch over to enable it - and save some battery as well.