umm well billing system is same as they have mentioned on website .. except that taxes which u have to pay .. i.e. sales tax .. advance tax and one more tax dont remember on the total usage ... over all comparing if ur calling r high then u should else u will be happy on prepaid ... as u have many upcoming promotions n all on prepaid .. not much on post paid ...
for example if u get hold to a 250 per month package then even if u dnt use .. u have to pay 250 + taxes on it ..