In India generally we will get itemised bill for postpaid connections and not for prepaid bills.
Incase if you need prepaid bills for a particular month, airtel will send prepaid bill to your email address when you request them. You will be charged Rs.50/- for this service. charging is done through deducting in your prepaid account balance. ( This charge is when i am writing this article Feb 2011).
send sms with below contents to the number 121
EPREBILL month_name mail_id
EPREBILL July email@example.com