You pay up-front, and at the end/start of the month. I got their wimax dongle on the 14th, and they only charged me till the end of month instead of the full monthly charge. This is for their wimax dongle - I don't know about the fibre. And if you were thinking of the wimax dongle, find someone who has it first and TEST IT first. I am VERY unhappy with mine - taking it back and cancelling end of this week!