i have always believed that the rates displayed on the screen are not necessarily linked to the congestion (or lack of it) of the network at that point in time.
it's possible the phone type (3g or 2g) may be part of the criteria for the disparity in rates even when standing right next to someone else.
the safcon people still want to maintain profitability even as they sell this seemingly cheaper rate to us,bearing this in mind it's then easy to conceptualise a myriad of ways to tinker with the rates so as to come to the same profitability they have always had.
If you are going to be thinking only one thing, you might as well be thinking big. -Donald J . Trump