You can deactivate Idea 3G service anytime to convert your sim card to 2G service. This is simple and easy. You have to send SMS to change your service type.
Send sms DEACT3G to 12345 . This is toll free number.
To know more about 3G services, to change tariff Plans and other information, please dial *147#
To turn off 3G plans for specific period on your phone, do the following steps-
Go to Settings
Select Network option
Select 2G network on handset
3G packs will be remain activated, but service will be from 2G network.
To deactivate plans, call customer care.