Buying things in units

In America, we're used to paying for utilities monthly in a bill. Here in Turkey, cell phone time is purchased in köntör (units), but, as near as I can tell, no one is quite sure how long you can talk per köntör, or how man text messages are in a köntör. People text here a lot because it's actually much cheaper than talking. This is sensible; text messages back home cost me 20 cents a piece, so don't text me, please. This is funny, because, byte for byte, data sent by text message is more expensive by a large factor than sending data to the space shuttle and back again. Natural gas is also purchased in units, rather than paid-for at the end of the month. Today, in the metro station at Kızılay, we saw many people standing in a long queue to pay for gas, which seems inefficient. I'm told that this is because many people only have enough money to pay for three or four days' worth of gas at a time.