Using this service since 2003. Till 2007 it was prepaid , had to convert it to postpaid in Oct 07. I have not yet faced any problem in billing.
I am getting detailed bill on my mail every month and did not need to call customer support till date . only problem is that idea doesn’t have cheap sms plan for postpaid connections. advantages : Call rates are competitive, have range of products in postpaid segment, and most important network is best, no call drops while driving.
Disadvantages : No cheap sms plan. 3g speed not up to the mark, ringtone cut off time is lesser than others.
Overall service is good I recommend idea in Maharashtra.