As you talk, send messages and use data, idea goes on calculating charges based on your plan rates. Say you have 100 rupee rental plan giving you 500 free minutes and calls at Re.1/min thereafter. Now, say within the first 7 days, you talk for a total of 100 minutes, then your unbilled will be 100*1 = 100 rupees at the end of the week. If you use a total of 1000 minutes at the end of the month. Your unbilled will be 1000*1= 1000 rupees. Now, when your bill is generated, idea will apply a discount of 500 minutes ie 500*1 = 500 rsYour bill = unbilled - discounts + taxBill = 1000 - 500 + tax